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ENGLAND

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Originally appearing in Volume V20, Page 556 of the 1911 Encyclopedia Britannica.
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ENGLAND. FRANCE, &C. Wanting Danian Upper Chalk Senonian Middle Chalk Turonian Lower Chalk Cenomanian Upper Green-sand Gault Albian Aptian Valenginian Urgonian Wealden Neocomian In the continental classification the deposits from the Gault downwards are grouped as Lower Cretaceous; but in Great Britain there is a strong break below the Gault and none above; and the Gault is therefore classed as Upper Cretaceous. The limits of the divisions in other places do not correspond, the British and continental strata often being so unlike that it is almost impossible to compare them. The doubt as to the exact British equivalent of the Valenginian strata of Portugal, which yield the earliest Dicotyledon, has already been alluded to. The plant-bearing deposits next in age, which have yielded Angiosperms, appear to belong to the Cenomanian, though from Westphalia a few species belonging to the Cryptogams and Gymnosperms, found in deposits correlated with the Gault, have been described by Hosius and von der Marck. In Great Britain the whole of the Upper Cretaceous strata are of marine origin, and have yielded no land-plants beyond a few fir-cones, drift-wood and rare Dicotyledonous leaves in the Lower Chalk. Most of the deposits which have yielded Angiosperms of Cretaceous age in central Europe correspond in age with the English Upper Chalk (Senonian), but a small Cenomanian flora has been collected from the Unter Quader in Moravia. Heer described from this deposit at Moletein 13 genera, of which 7 are still living, containing 18 species, viz.: t fern, 4 Conifers, I palm, 2 figs, I Credneria, 2 laurels, I Aralia, I Chondrophyllum (of uncertain affinities), 2 magnolias, 2 species of Myrtaceae and a species of walnut. Saxony yields from strata of this period at Niederschoena 42 species, de-scribed by Ettingshausen. This small flora is most remarkable, for no fewer than 6 genera, containing 8 species, are referred to the Proteaceae. The Cenomanian flora of Bohemia is larger and equally peculiar. Among the Dicotyledons described by Velenovsky are the following: Credneria (5 species), Araliaceae (17 species), Proteaceae (8 species), Myrica (2 species), Ficus (5 species), Quercus (2 species), Magnoliaceae (5 species), Bombaceae (3 species), Laurineae (2 species), Ebenaceae (2 species), Verbenaceae, Conibretaceae, Sapindaceae (2 species), Camelliaceae, Ampelideae, Mimoseae, Caesalpinieae (5 species), Eucalyptus (2 species), Pisonia, Phillyrea, Rhus, Prunus, Bignonia, Lower Green-sand Laurus, Salix, Benthamia. To this list Bayer adds Aristolochia. The Cenomanian flora of central Europe appears to be a sub-tropical one, with marked approaches to the living flora of Australia. The majority of its Dicotyledons belong to existing genera, but one of the most prolific and characteristic Cretaceous forms is Credneria (Fig. 3), a genus of doubtful affinities, which has been compared by different authors to the poplars; planes, limes and other orders. The Cretaceous plant-beds of Westphalia include both Upper and Lower Senonian, the two floras being very distinct. Hosius and von der Marck describe, for instance, 12 species of oak from the Upper and 6 from the Lower strata, but no species is common to the two. The same occurs with the figs, with 3 species above and 8 below. The 6 species of Credneria are all confined to the older deposits. In fact, not a single Dicotyledon is common to these two closely allied divisions of the Cretaceous series; a circumstance not easy to explain, when we see how well the oaks and figs are represented in each. Four species of Dewalquea, a ranunculaceous genus allied to the hellebore, make their appearance in the Upper Senonian of Westphalia, other species occurring at Aix-la-Chapelle in deposits of about the same age. The Senonian flora of the last-named place, and that of Maestricht, are still only imperfectly known. It is unnecessary to trace the variations of the Upper Cretaceous flora from point to point; but the discoveries within the Arctic circle have been so surprising that attention must again be called to them. Besides the Lower Cretaceous plants already mentioned, Heer has described from Greenland a flora of Cenomanian age, and another belonging to the Senonian. The Cenomanian strata have yielded already 177 species, the different groups being represented in these proportions: Cryptogams, 37, 30 of which are Ferns ; Cycads, 8 ; Conifers, 27 ; Monocotyledons, 8 ; Ape-talons Dicotyledons, 31; other Dicotyledons, 66. The Senonian strata have yielded 118 species, 21 of which are Cryptogams, 11 Conifers, 5 Monocotyledons, 75 Dicotyledons. Forest trees, especially oaks, are plentiful, and many of the species are identical with those found in Cretaceous deposits in more southern latitudes. Both of these floras suggest, however, that the climate of Greenland was some-what colder than that of Westphalia, though scarcely colder than warm-temperate. The Cretaceous deposits just described are followed by a series of Tertiary formations, but in Europe the continuity between Cretaceous and Tertiary is not quite complete. The Tertiary formations have been assigned to six periods; these are termed—Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and each has its own botanical peculiarities. During the Paleocene period the plants were not markedly different from those of the Upper Cretaceous. Its flora is still but imperfectly known, for we are dependent on two Paleocene or three localities for the plants. There is found at Plants. Sezanne, about 6o m. east of Paris, an isolated deposit of calcareous tufa full of leaves, which gives a curious insight into the vegetation which flourished in Paleocene times around a waterfall. Sezanne yields Ferns in profusion, mingled with other shade-loving plants such as would grow under the trees in a moist ravine; its vegetation is comparable to that of an island in the tropical seas. Monocotyledons are rare, the only ones of much interest being some fragments of pandanaceous leaves. The absence of Gymnosperms is noticeable. The Proteaceae are also missing; but other Dicotyledons occur in profusion, many of them being remarkable for the large size of their deciduous leaves. Among the flowering plants are Dewalquea, a ranunculaceous genus already mentioned as occurring in the Upper Cretaceous, and numerous living genera of forest-trees, such as occur throughout the Tertiary period, and are readily comparable with living forms. Saporta has described about seventy Dicotyledons, most of which are peculiar to this locality. The plant-bearing marls of Gelinden, near Liege, contain the debris of a Paleocene forest. The trees seemed to have flourished on neighbouring chalky heights. The most abundant species of this forest were the oaks and chestnuts, of which a dozen have been collected; laurels, Viburnum, ivy, several Aralias, Dewalquea, a Thuja and several Ferns may be added. This flora is compared by Saporta and Marion with that of southern Japan. Other de-posits of this age in France have furnished plants of a more varied aspect, including myrtles, araucarias, a bamboo and several fan-leaved palms. Saporta points out the presence in these Paleocene deposits of certain types common, on the one hand, to the American Tertiary strata between the Missouri and the Rocky Mountains, and on the other, to the Tertiary flora of Greenland. The Paleocene deposits of Great Britain are of marine origin, and only yield pine-cones and fragments of Osmunda. The British Eocene and Oligocene strata yield so large a flora, and contain plant-beds belonging to so many different stages, that it is unfortunate we have still no monograph on the subject, the one commenced by Ettingshausen Eocene and and Gardner in 1879 having reached no farther than ooffig(treareat t the Ferns and Gymnosperms. This deficiency Britain, makes it impossible to deal adequately with the British Eocene plants, most of the material being either unpublished or needing re-examination. In the earliest Eocene plant-beds, in the Woolwich and Reading series, a small but interesting flora is found, which suggests a temperate climate less warm than that of earlier or of later periods. Leaves of planes are abundant, and among the plants recorded are two figs, a laurel, a Robinia, a Grevillea and a palm. Ferns are scarce, Ettingshausen and Gardner recording only Aneimia subcretacea and Pteris (?) Prestwichii. The only Gymnosperms determined are Libocedrus adpressa, which is close to L. decurrens of the Yosemite, and Taxodium europaeum. A few plants have been found in the next stage, the Oldhaven beds, and among these are fig and cinnamon: Gardner considers the plants to point to subtropical conditions. The London Clay has yielded a large number of plants, but most of the species are represented by fruits alone, not by leaves. This circumstance makes it difficult to compare the flora with that of other formations, for not only is it uncertain which leaves and fruits belong to the same plant, but there is the additional source of doubt, that different elements of the same flora may he represented at different localities. Of some plants only the deciduous leaves are likely to be preserved, whilst other succulent-leaved forms will only be known from their woody fruits. Among the 200 plants of the London Clay are no Ferns, but 6 genera of Gymnosperms—viz. Callitris (2 species), Sequoia, Athrotaxis (?) Ginkgo, Podocar pus, Pinus; and several genera of palms, of which the tropical Nipa is the most abundant and most characteristic, among the others being fan-palms of the genera Sabal and Chamaerops. The Dicotyledons need further study. Among the fruits Ettingshausen records Quercus, Liquidambar, Laurus, Nyssa, Diospyros, Symplocos, Magnolia, Victoria, Hightea, Sapindus, Cupania, Eugenia, Eucalyptus, Amygdalus; he suggests that the fruits of the London Clay of Sheppey may belong to the same plants as the leaves found at Alum Bay in the Isle of Wight. The next stage is represented by the Lower Bagshot leaf-beds of Alum Bay. These pipeclays yield a varied flora, Ettingshausen recording 274 species, belonging to 116 genera and 63 families. Gardner, however, is unable to reconcile this estimated richness with our knowledge of the flora, and surmises that fossil plants from other localities must have been inadvertently included. He considers the flora to be the most tropical of any that has so far been studied in the northern hemisphere. Its most conspicuous plants are Ficus Bowerbankii, Aralia primigenia, Comptonia acutiloba, Dryandra Bunburyi, Cassia Ungeri and the fruits of Caesalpinia. The floras which it chiefly resembles are first, that of Monte Bolca, and second, that of the Gres du Soissonais, which latter Gardner thinks may be of the same age, and not earlier, as is generally supposed. The total number of species found at Alum Bay, according to this author, is only about 5o or 6o. To the Bagshot Sand succeeds the thick mass of sands with intercalated plant-beds seen in Bournemouth cliffs. Each bed yields peculiar forms, the total number of species amounting to many hundred, most of them differing from those occurring in the strata below. The plants suggest a comparison of the climate and forests with those of the Malay Archipelago and tropical America. At one place we find drifted fruits of Nipa, at another Hightea and Anona. Other beds yield principally palms, willows, laurels, Eucalyptus or Ferns; but there are no Cycads. As showing the richness of this flora, we may mention that in the only orders which have yet been monographed, Ferns are represented by 17 species and Gymnosperms by io, though these are not the groups best represented. Gardner speaks of the Bournemouth flora as appearing to consist principally of trees or hard-wooded shrubs, comparatively few remains of the herbaceous vegetation being preserved. The higher Eocene strata of England—those above the Bournemouth Beds—are of marine origin, and yield only drifted fruits, principally fir-cones. In the volcanic districts of the south-west of Scotland and the north-east of Ireland plant-beds are found intercalated between the lava-flows. These also, like the lignites of Bovey Tracey, have been referred to the Miocene period, on the supposed evidence of the plants; but more recent discoveries by Gardner tend to throw doubt on this allocation, and suggest that, though of various ages, the first-formed of these deposits may date back to early Eocene times. The flora found in Mull points distinctly to temperate conditions; but it is not yet clear whether this indicates a different period from the subtropical flora of the south of England, or whether the difference depends on latitude or local conditions. The plants include a Fern, Onoclea hebridica, close to a living American form ; four Gymnosperms belonging to the genera Cryptomeria, Ginkgo, Taxus and Podocarpus; Dicotyledons of about 30 species, several of which have been figured. Among the Dicotyledons may be mentioned Platanus, Acer (?), Quercus (?), Viburnum, Alnus, Magnolia, Corylus (?), Castanea (?), Zizyphus, Populus and the nettle-like Boehmeria antiqua. The absence cf the so-called cinnamon-leaves and the Smilaceae, which always enter into the composition of Middle Eocene and Oligocene floras, is notice-able. The Irish strata yield two ferns; 7 Gymnosperms, Cupressus, Cryptomeria, Taxus, Podocarpus, Pinus (2 species), Tsuga; and leaves of about 25 Dicotyledons. The most abundant leaf, according to Gardner, does not seem distinct from Celastrophyllum Benedeni, of the Paleocene strata of Gelinden; a water-lily, Nelumbium Buchii, occurs also in Oligocene beds on the Continent; the species of MacClintockia (fig. 4) is found both in the Arctic floras and at Gelinden. Among the other plants are an alder, an oak and a doubtful cinnamon. Leaving these Scottish and Irish deposits of doubtful age, we find in the Hampshire Basin a thick series of fluviatile, lacustrine and marine deposits undoubtedly of Lower and Middle Oligocene date. Their flora is still a singularly poor one, though plants have been obtained at many different levels; they perhaps indicate a somewhat cooler climate than that of the Bournemouth series. Among the more abundant plants are nucules of several species of Chara, and drifted fruits and seeds of water-lilies, of Folliculites (now generally referred to Stratiotes) and of Limnocarpus (allied to Potamogeton) ; there is little else mixed with these. Other seams are full of the twigs and cones of Athrotaxis, a Conifer now confined to Tasmania. Ferns are represented by Gleichenia, Lygodium and Chrysodium Lanzaeanum, which last has a very wide range in time; Monocotyledons, by a Sabal and a feather-palm, as well as by the two aquatic genera above mentioned; Gymnosperms. by the extinct araucarian genus Doliostrobus, by rare pine-cones, and by Athrotaxis. Dicotyledonous leaves are not plentiful, the genera recorded being Andromeda, Cinnamomum, Zizyphus, Rhus, Viburnum. The lignite deposits and pipe-clays of Bovey Tracey in Devon, referred by Heer and Pengelly to the Miocene period, were considered by Gardner to be of the same age as the Bournemouth beds (Middle Eocene). Recent researches show, however, that Heer's view was more nearly correct. The flora of Bovey is like that of the lignite of the Wetterau, which is either highest Oligocene or lowest Miocene. Several species of Nyssa are common to the two districts, as are a climbing palm, two vines, a magnolia, &c. The common tree at Bovey is Sequoia Couttsiae, which probably grew in profusion in the sheltered valleys of Dartmoor, close to the lake. Above these strata in Great Britain there is a complete break, no species of plant ranging upwards into the next fossiliferous division. central and that met with in other geographical regions and in Southern France. other latitudes. For this study it will be most convenient to take next south and central France, for in that area can be found a series of plant-bearing strata in which is preserved a nearly continuous history of the vegetation from Upper Eocene down to Pliocene. The account is taken mainly from the writings of Saporta. The gypsum-deposit of Upper Eocene date at Aix in Provence commences this series, and is remarkable for the variety and perfect preservation of its organic remains. Among its Gymnosperms are numerous Cupressineae of African affinity belonging to the genera Callitris and Widdringtonia, and a juniper close to one indigenous in Greece. Fan-palms, several species of dragon-tree and a banana, like one living in Abyssinia, represent the more peculiar Mono-cotyledons. Among the noticeable Dicotyledons are the Myricaceae, Proteaceae, Laurineae, Bombax, the Judas-tree, Acacia, Ailanthus, while the most plentiful forms are the Araliaceae. Willows and poplars, with a few other plants of more temperate regions, are found rarely at Aix, and seemingly point to casual introduction from surrounding mountains. In a general way, spiny plants, with stiff branches and dry and coriaceous leaves, dominate theflora, as they now do in Central Africa, to which region on the whole Saporta considers the flora to be most allied. The succeeding Oligocene flora appears to. be more characterized by a gradual replacement of the Eocene species by allied forms, than by any marked change in the assemblage or in the climatic conditions. It forms a perfectly gradual transition to the still newer Miocene period, the newer species slowly appearing and increasing in number. Saporta considers that in central and southern Europe the alternate dry and moist heat of the Eocene period gave place to a climate more equally and more universally humid, and that these conditions continued without material change into the succeeding Miocene stage. Among the types of vegetation which make their appearance in Europe during the Oligocene period may be mentioned the Conifers Libocedrus salicornioides, several species of Chamaecyparis and Sequoia, Taxodium distichum and Glyptostrobus europaeus. The palms include Sabal haeringiana, S. major and Flabellaria. Among the Myricaceae several species of Comptonia are common. These new-corners are all of American type. Aquatic plants, especially water-lilies, are abundant and varied; the soil-dry Callitris and Widdringtonia become scarce. Though we do not propose to deal with the other European localities for Eocene and Oligocene plants, there is one district to which attention should be drawn, on account of the exceptional state of preservation of the specimens. plantser m Amb On the Baltic shores of Prussia there is found a quantity of amber, containing remains of insects and plants. This is derived from strata of Oligocene age, and is particularly valuable because it preserves perfectly various soft parts of the plants, which are usually lost in fossil specimens. The tissues, in fact, are preserved just as they would be in .Canada balsam. The amber yields such things as fallen flowers, perfect catkins of oak, pollen grains and fungi. It enables us to determine accurately orders and genera which otherwise are unknown in the fossil state, and it thus aids us in forming a truer idea of the flora of the period than can be formed at any locality where the harder parts alone are recognizable. No doubt this amber flora is still imperfectly known, but it is valuable as giving a good idea of the vegetation, during Oligocene times, of a mixed wood of pine and oak, in which there is a mixture of herbaceous and woody plants, such as would now be found under similar conditions. The plants of which the floral organs or perfect fruits are pre-served include the amber-bearing Pinus succinifera, Smilax, Phoenix, the spike of an aroid, II species of oak, 2 of chestnut, a beech, Urticaceae, 2 cinnamons and Trianthera among the Lauraceae, representatives of the Cistaceae, Ternstroemiaceae, Dilleniaceae (3 species of Hibbertia), Geraniaceae (Geranium and Erodium), Oxalidaceae, Acer, Celastraceae, Olacaceae, Pittosporaceae, Ilex (2 species), Euphorbiaceae, Umbelliferae (Chaerophyllum), Saxifragaceae (3 genera), Hamamelidaceae, Rosaceae, Connaraceae, Ericaceae (Andromeda and Clethra), Myrsinaceae (3 species), Rubiaceae, Sambucus (2 species), Santalaceae, Loranthaceae (3 species). We here discover for the first time various living families and genera, but there is still a noticeable absence of many of our most prolific existing groups. Whether this deficiency is accidental or real time will show. The Miocene flora, which succeeds to that just described, is well represented in Europe; but till recently there has been an unfortunate tendency to refer Tertiary floras of all Miocene. dates to the Miocene period, unless the geological position of the strata was so clear as obviously to forbid this assignment. Thus plant-beds in the basalt of Scotland and Ireland were called Miocene; and in the Arctic regions and in North America even plant-beds of Upper Cretaceous age were referred to the same period. The reason for this was that some of the first Tertiary floras to be examined were certainly Miocene, and, when these plants had been studied, it was considered that somewhat similar assemblages found elsewhere in deposits of doubtful geological age must also be Miocene. For a long time it was not recognized that changes in the marine fauna, on which our geological classification mainly depends, correspond scarcely at all with changes in the land plants. It was not suspected, or the fact was ignored, that the break between Cretaceous and Tertiary—made so conspicuous by striking changes in the aquatic animals—had little or no importance in botanical history. It was not realized that an Upper Cretaceous flora needed critical examination to distinguish it from one of Miocene age, and that the two periods were not characterized by a Space will not allow us to deal with the numerous scattered deposits which have yielded Tertiary plants. It will be more to the purpose to take distant areas, where the order of the strata is clear, and compare the succession of the floras with sweeping change of generic type, such as took place among the marine invertebrates. It may appear absurd to a geologist that any one could mistake a Cretaceous flora for one of Miocene date, since the marine animals are completely different and the differences are striking. In the case of the plants, however, the Tertiary generic types in large part appeared in Upper Cretaceous times. Few or no extinct types are to be found in these older strata—there is nothing among the plants equivalent to the unmistakably extinct Ammonites, Belemnites, and a hundred other groups, and we only meet with constant variations in the same genus or family, these variations having seldom any obvious relation to phylogeny. The Miocene period is unrepresented by any deposits in Great Britain, unless the Bovey lignite should belong to its earliest stage; we will therefore commence with the best known region—that of central Europe and especially of Switzerland, whence a prolific flora has been collected and described by Oswald Heer. The Miocene lacustrine deposits are contained in a number of silted-up lake-basins, which were successively formed and obliterated during the uprise of the Alps and the continuous folding and bending of the earth's crust which was so striking a feature of the period. These undulations tended to transform valleys into chains of lakes, into which the plants and animals of the surrounding area fell or were washed. We thus find preserved in the Upper Miocene lacustrine deposits of Switzerland a larger flora than is known from any other period of similar length; in fact, an analysis of its composition suggests that the Miocene flora of Switzerland must have been both larger and more varied than that now living in the same country. The best known locality for the Upper Miocene plants is Oeningen, on the Lake of Constance, where have been collected nearly 50o species of plants, the total number of Miocene plants found in Switzerland being stated to be now over 900. Among the characteristics of this Miocene flora are the large number of families represented, the marked increase in the deciduous-leaved plants, the gradual decrease in the number of palms and of tropical plants, and the replacement of these latter by Mediterranean or North American forms. According to Heer, the tropical forms in the Swiss Miocene agree rather with Asiatic types, while the subtropical and temperate plants are allied to forms now living in the temperate zone in North America. Of the 920 species described by Heer, 114 are Cryptogams and 806 flowering plants. Mosses are extremely rare, Heer only describing 3 species. Vascular Cryptogams still include one or two large horsetails with stems over an inch thick, and also 37 species of Fern, amongst the most interesting of which are 5 species belonging to the climbing Lygodium, a genus now living in Java. The number of Ferns is just equal to that now found in Switzerland. Cycads are only represented by fragments of two species, and this seems to be the last appearance of Cycads in Europe. The Coniferae include no fewer than 94 species of Cupressineae and 17 of Abietineae, including several species of Sequoia. Monocotyledons form one-sixth of the known Miocene flora, 25 of them being grasses and 39 sedges; but most of these need further study, and are very insufficiently characterized. Heer records one species of rice and four of millet. Most of the other Monocotyledons call for little remark, though among them is an Iris, a Bromelia and a ginger. Smilax, as in earlier times, was common. Palms, referred to i i species, are found, though they seem to have decreased in abundance; of them 7 are fan-palms, the others including Phoenicites—a form allied to the date—and a trailing palm, Calamopsis, allied to the canes and rattans. Among the Dicotyledons, the Leguminosae take the first place with 131 species, including Acacia, Caesalpinia and Cassia, each represented by several forms. The occurrence of 90 species of Amentaceae shows that, as the climate became less tropical, the relative proportion of this group to the total flora increased. Evergreen oaks are a marked characteristic of the period, more than half the Swiss species being allied to living American forms. Fig-trees referred to 17 species occur, all with undivided leathery leaves; one is close to the banyan, another to the indiarubber-tree The Laurineae were plentiful, and include various true laurels, camphor-trees, cinnamon, Persea and Sassafras. The Proteaceae, according to Heer, are still common, the Australian genera Hakea, Dryandra, Grevillea and Banksia, being represented. Amongst gamopetalous plants several of our largest living families, including Campanulaceae, Labiatae, Solanaceae and Primulaceae, are still missing; and of Boragineae, Scrophularineae, Gentianeae and Caprifoliaceae there are only faint and doubtful indications. The Cotnpositae are represented by isolated fruits of various species. Twining lianas are met with in a species of Bignonia; Umbelliferae Ranunculaceae and Cruciferae, are represented by a few fruits. These families, however, do not appear to have had anything like their present importance in the temperate flora, though, as they are mainly herbaceous plants with fruits of moderate hardness, they may have decayed and left no trace. The American Liriodendron still flourished in Europe. Water-lilies of the genera Nymphaea and Nelumbium occur. Maples were still plentiful, 20 specieshaving been described. Rosaceae are rare, Crataegus, Prunus and Amygdalus, being the only genera recorded. It is obvious that many of these Swiss Miocene plants will need more close study before their specific characters, or even their generic position, can be accepted as thoroughly made out; still, this will not affect the general composition of the flora, with its large proportion of deciduous trees and evergreens, and its noticeable deficiency in many of our largest living families. From Europe it will be convenient to pass to a distant region of similar latitude, so that we may see to what extent botanical provinces existed in Eocene and Oligocene times. It Tertiary so happens that the interior of temperate North of North America is almost the only region outside Europe in Amer" which a series of plant-bearing strata give a connected history of these periods, and in which the plants have been collected and studied. It is unfortunately still very difficult to correlate even approximately the strata on the two sides of the Atlantic, and there is great doubt as to what strata belong to each division of the Tertiary period even in different parts of North America. This difficulty will disappear as the strata become better known; but at present each of the silted-up lakes has to be studied separately, for we cannot expect so close a correspondence. in their faunas and floras as is found in the more crowded and smaller basins in central Europe. Perhaps the most striking characteristic of the Tertiary floras of North America, as distinguished from those of Europe, is the greater continuity in their history and greater connexion with the existing flora of the same regions. This difference is readily explained when we remember that in Europe the main barriers which stop migration, such as the Alps and the Mediterranean, run east and west, while in America the only barriers of any importance run north and south. In consequence of this peculiarity, climatic or orographic changes in Europe tend to drive animals and plants into a cul de sac, from which there is no escape; but in America similar climatic waves merely cause the species alternately to retreat and advance. .This difficulty in migration is probably the reason why the existing European flora is so poor in large-fruited trees compared with what it was in Miocene times or with the existing flora of North America. In America the contrast between the Eocene forests and those now living is much less striking, and this fact has led to the wrong assumption that the present American flora had its origin in the American continent. Such a conclusion is by no means warranted by the facts, for in Tertiary times, as we have seen, the European flora had a distinctly " American " facies. Therefore the so-called American forms may have originated in the Old World, or more probably, as Saporta suggests, in the polar regions, whence they were driven by the increase of cold southwards into Europe and into America. The American Tertiary flora is so large, and the geology of the deposits is so intricate, that it is out of the question to discuss them more fully within the limits of this article. We may point out, however, that the early Tertiary floras seem to indicate a much closer connexion and a greater community of species than is found between the existing plants of Europe and America. Or, rather, we should perhaps say that ancient floras suggest recent dispersal from the place of origin, and less time in which to vary and become modified by the loss of different groups in the two continents. Geographical provinces are certainly indicated by the Eocene flora of Europe and America, but these are less marked than those now existing. If we turn to a more isolated region, like Australia, we find a Lower Eocene flora distinctly related to the existing flora of Australia and not to that of other continents. Australasia had then as now a peculiar flora of its Australia. own, though the former wide dispersal of the Proteaceae and Myrtaceae, and also the large number of Amentaceae then found in Australia, make the Eocene plants of Europe and Australia much less unlike than are the present floras. Within the Arctic circle a large number of Tertiary plants have been collected. These were described by Heer, who referred them to the Miocene period; he recognized, Arctic in fact, two periods during which Angiosperms Regions. flourished within the Arctic regions, the one Upper Cretaceous, the other Miocene. To this view of the Miocene age of the plant-bearing strata in Greenland and Spitsbergen there are serious objections, which we will again refer to when the flora has been described. The Tertiary flora of Greenland is of great interest, from the extremely high latitude at which the plants flourished, thirty of the species having been collected so far north as lat. 81°. Taking first this most northerly locality, in Grinnell Land, we find the flora to comprise 2 horsetails, 11 Conifers (including the living Pinus Abies), 2 grasses, a sedge, 2 poplars, a willow, 2 birches, 2 hazels, an elm, a Viburnum, a water-lily, and a lime. Such an assemblage at the present day would suggest a latitude quite 25° farther south; but it shows decidedly colder conditions than any of the European Eocene, Oligocene, or Miocene strata. From lat. 78° in Spitsbergen Heer records 136 species of fossil plants. More to the south, at Disco Island in lat. 70°, the Tertiary wood seem to have been principally composed of planes and Sequoias; but a large number of other genera occur, the total number of plants already recorded being 137. From various parts of Greenland they now amount to at least 280. Among the plants from Disco, more than a quarter are also found in the Miocene of central Europe. The plants of Disco include, besides the plane and Sequoia, such warm-temperate trees as Ginkgo, oak, beech, poplar, maple, walnut, lime and magnolia. If these different deposits are contemporaneous, as is not improbable, there is a distinct change in the flora as we move farther from the pole, which suggests that difference of latitude then as now was accompanied by a difference in the flora. But if this process is continuous from latitude to latitude, then we ought not to look for a flora of equivalent age in the warm-temperate Miocene deposits of central Europe, but should rather expect to find that the temperate plants of Greenland were contemporaneous with a tropical flora in central Europe. As Mr Starkie Gardner has pointed out, it does not seem reasonable to assume that the same flora could have ranged then through 40° of latitude; it is more probable that an Eocene temperate flora found in the Arctic regions travelled south-wards as the climate became cooler, till it became the Miocene temperate flora of central Europe. Mr Gardner suggests, therefore, that the plant-beds of Greenland and Spitsbergen represent the period of greatest heat, and are therefore wrongly referred to the Miocene. At present the evidence is scarcely sufficient to decide the question, for if this view is right, we ought to find within the Arctic circle truly Arctic floras equivalent to the cool Lower Eocene and Miocene periods; but these have not yet been met with. A steady decrease of temperature marked the Pliocene period throughout Europe, and gradually brought the climatic con- Piiocene. ditions into correspondence with those now existing, till towards the end of the period neither climate nor physical geography differed greatly from those now existing. Concurrently with this change, the tropical and extinct forms disappeared, and the flora approached more and more nearly to that now existing in the districts where the fossil plants are found, though in the older deposits, at any rate, the geographical distribution still differed considerably from that now met with. At last, in the latest Pliocene strata (often called " pre-Glacial ") we find a flora consisting almost entirely of existing species belonging to the Palaearctic regions, and nearly all still living in the country where the fossils are found. This flora, however, is associated with a fauna of large mammals, the majority of which are extinct. The plants of the Older Pliocene period are unknown in Great Britain, and little known throughout Europe except in central France and the Mediterranean region. The forests of central France during this epoch showed, according to Saporta, a singular admixture of living European species, with trees now characteristic of the Canary Isles and of North America. For instance, of the living species found at Meximieux, near Lyons, one is American, eight at least belong to the Canaries (six being characteristic of those islands), two are Asiatic, and ten still live in Europe. Taking into account, however, the closest living allies of the fossil plants, we find about equal affinities with the floras of Europe, America, and Asia. There is also a decided resemblance to the earlier Miocene flora. Among the more interesting plants of this deposit may be mentioned Torreya nucifera, now Japanese; an evergreen oak close to the common Quercus Ilex; Laurus canariensis, Apollonias canariensis, Persea carolinensis, and Ilex canariensis; Daphne pontica (a plant of Asia Minor); a species of box, scarcely differing from the English, and a bamboo. To this epoch, or perhaps to a stage slightly later, and not to the Newer Pliocene period, as is generally supposed, should probably be referred the lignite deposits of the Val d'Arno. This lignite and the accompanying leaf-bearing clays underlie and are apparently older than the strata with Newer Pliocene mammals and mollusca. The only mammal actually associated with the plants appears to be a species of tapir, a genus which in Europe seems to be characteristically Miocene and Older Pliocene. The plants of the Val d'Arno have been described by Ristori; they consist mainly of deciduous trees, a large proportion of which are known Miocene and early Pliocene forms, nearly all of them being extinct. A markedly upland character is given to the flora of this valley through the abundance of pines (9 species) and oaks (16 species) which it contains; but this peculiarity is readily accounted for by the steep slopes of the Apennines, which everywhere surround and dominate the old lake-basin. Among the other noticeableplants may be mentioned Betula (3 species), Alnus (2 species), Carpinus, Fagus (4 species), Salix (4 species), Populus (2 species), Platanus, Liquidambar, Planera, Ulmus (2 species), Ficus (2 species), Persoonia, Laurus (5 species), Persea, Sassafras, Cinnamomum (5 species), Oreodaphne, Diospyros (2 species), Andromeda, Magnolia, Ater (3 species), Sapindus, Celastrus (2 species), Ilex (4 species), Rhamnus (3 species), Juglans (5 species), Carya (2 species), Rhus, Myrtus, Crataegus, Prunus, Cassia (3 species). These plants suggest a colder climate than that indicated by the plants of Meximieuxthey might, therefore, be thought to belong to a later period. The difference, however, is probably fully accounted for when we take into consideration the biting winds still felt in spring in the valley of the Arno, and the probable large admixture of plants washed down from the mountains above. Somewhat later Pliocene deposits in the Val d'Arno, as well as the tuffs associated with the Pliocene volcanoes in central France, yield plants of a more familiar type, a considerable proportion of them still living in the Mediterranean region, though some are only now found at distant localities, and others are extinct. The flora, however, is essentially Palaearctic, American and Australian types having disappeared. A somewhat later Pliocene flora is represented by the plants found at Tegelen, near Venloo, on the borders of the Netherlands and Germany. This deposit is of especial interest for the light it throws on the origin of the existing flora of Britain. The Tegelen plants are mainly north European; but there occur others of central and south Europe, and various exotic and extinct forms, nearly all of which, however, belong to the Palaearctic region, though some may now be confined to widely separated parts of it. For instance, Pterocarya caucasica does not grow nearer than the Caucasus, where it is associated with the wild vine—also found at Tegelen; Magnolia Kobus is confined to the north island of Japan; another species of Magnolia cannot be identified and may be extinct. An extinct water-lily, Euryale limburgensis, belongs to a monotypic genus now confined to Assam and China; an extinct sedge, Dulichium vespiforme, belongs to a genus only living in America, though the only living species once flourished also in Denmark; an extinct species of water-aloe (Stratiotes elegans) makes a third genus, represented only by a single living species, which was evidently better represented in Pliocene times. A large proportion of the plants, however, may still be found living in Holland and Britain; but there is a singular scarcity of Composites, though this order is fairly well represented in British strata of slightly later date. The latest Pliocene, or pre-Glacial, flora of northern Europe is best known from the Cromer Forest-bed of Norfolk and Suffolk, a fluvio-marine deposit which lies beneath the whole of the Glacial deposits of these counties, and passes downwards into the Crag, many of the animals actually associated with the plants being characteristic Pliocene species which seem immediately afterwards to have been exterminated by the increasing cold. The plants contained in the Cromer Forest-bed, of which about 15o species have now been determined, fall mainly into two groups—the forest-trees, and marsh and aquatic plants. We know little or nothing at present of the upland plants, or of those of dry or chalky soils. Forest trees are well represented; they are, in fact, better known than in any of the later English deposits. We find the living British species of Rhamnus, maple, sloe, hawthorn, apple, white-beam, guelder-rose, cornel, elm, birch, alder, hornbeam, hazel, oak, beech, willow, yew and pine, and also the spruce. This is an assemblage that could not well be found under conditions differing greatly from those now holding in Norfolk; there is an absence of both Arctic and south European plants. The variety of trees shows that the climate was mild and moist. Among the herbaceous plants we find, mingled with a number that still live in Norfolk, Hypecoum procumbens, the water-chestnut (Trapa natans), and Najas minor, none of which is now British. On the Norfolk coast another thin plant-bed occurs locally above the Forest-bed and immediately beneath the Boulder Clay. This deposit shows no trace of forest-trees, but it is full of remains of Arctic mosses, and of the dwarf willow and birch ; in short, it yields the flora now found within the Arctic circle. The incoming of the Glacial epoch does not appear to have been accompanied by any acclimatization of the Dlants—the species belonging to temperate Europe were locallymeistocene. exterminated, and Arctic forms took their places. The same Arctic flora reappears in deposits immediately above the highest Boulder Clay, deposits formed after the ice had passed away. These fossil Arctic plants have now been found as far south as Bovey Tracey in Devonshire, where Pengelly and Heer discovered the bear-berry and dwarf birch; London, where also Betula nana occurs; and at Deuben in Saxony, which lies nearly as far south as lat. 5o°, but has yielded to Professor Nathorst's researches several Arctic species of willow and saxifrage. The cold period, however, was not continuous, for both in Great Britain and on the continent of Europe, as well as in Canada, it was broken by the recurrence of a milder climate and the reappearance of a flora almost identical with that now living in the same regions. This " inter-Glacial " flora, though so like that now found in the district, has interesting peculiarities. In England, for instance, it includes Acer monspessulanum, a southern maple which does not now extend nearer than central Europe, and Cotoneaster Pyracantha; also Najas graminea and N. minor, both southern forms not now native of Britain. Brassenia peltata, a water-lily found in the warmer regions almost throughout the world, except in Europe, occurs abundantly in north Germany, but not in Great Britain. Similar inter-Glacial deposits in Tirol contain leaves of Rhododendron ponticuin. Space will not permit us to enter into any full discussion of the recurrence of Glacial and inter-Glacial periods and the influence they may have had on the flora. It is evident, how-ever, that if climatic alternations, such as those just described, are part of the normal routine that has gone on through all geological periods, and are not merely confined to the latest, then such changes must evidently have had great influence on the evolution and geographical distribution both of species and of floras. Whether this was so is a question still to be decided, for in dealing with extinct floras it is difficult to decide, except in the most general way, to what climatic conditions they point. We seem to find indications of long-period climatic oscillations in Tertiary times, but none of the sudden invasion of an Arctic flora, like that which occurred during more recent times. It should not be forgotten, however, that an Arctic flora is mainly distinguishable from a temperate one by its poverty and dwarfed vegetation, its deciduous leaves and small fruits, rather than by the occurrence of any characteristic genera or families. Careful and long-continued study would therefore be needed before we could say of any extinct dwarfed flora that it included only plants which could withstand Arctic conditions. AuruoRlrlES.—H. Conwentz, Monographie der baltiSchen Bernsteinbaume (Danzig, 1890), Die Flora des Bernsteins, vol. ii. (1886) ; Sir W. Dawson, Papers on the Cretaceous Plants of British North America, Trans. Roy. Soc. Canada (1883-1896); C. von Ettingshausen, Die Kreideflora von Niederschona in Sachsen," Sift. le. Akad. Wiss. Wien, math.-nat. Cl., vol. lv., Abth. i. (1867) ; " Report on . . . Fossil Flora of Sheppy," Proc. Roy. Soc. xxix. 388 (1879) ; Report on . Fossil Flora of Alum Bay," ibid. xxx. 228 (188o) ; C. von Ettingshausen and J. S. Gardner, " Eocene Flora," vols. i. and ii., Palaeont. Soc. (1879-1886) ; W. M. Fontaine, " The Potomac or Younger Mesozoic Flora," U.S. Geological Survey, Monograph xv. (1889) ; J. S. Gardner, Flora of Alum Bay, in " Geology of the Isle of Wight," Mem. Geol. Survey (2nd ed., 1889); H. R. Goeppert and A. Menge, Die Flora des Bernsteins and ihre Beziehungen zur Flora der Tertiarformation and der Gegenwart, vol. i. (Danzig, 1883); 0. Heer, Flora tertiaria ilehetiae (3 vols., Winterthur, 1855-1859) ; Flora fossilis arctica (7 vols., Zurich, 1868-1883), " Beitrage zur Kreideflora,—(1) Flora von Moletein in Mahren," New Denkschr. allgem. schweiz. Gesell. Naturwiss., vol. xxiii. mem. 22 (Zurich, '869-1872); Primaeval World in Switzerland (2 vols., '876); F. H. Knowlton, ' Catalogue of the Cretaceous and Tertiary Plants of North America," Bull. U.S. Geol. Survey (No. 152, 1898), " Flora of the Montana Formation," ibid., No. 163 (19oo); Krasser, " Die fossile Kreideflora von Kunstadt in Mahren,' Beit. paleont. Geol. Oesterreich-Ungarns, Bd. v. Hft. 3 (1896); Leo. Lesquereux, " Contributions to the Fossil Flora of the Western Territories," Rep. U.S. Geol. Survey of the Territories, vols. vi., vii., viii. (1877-1883), " The Flora of the Dakota Group," U.S. Geological Survey, Monograph xvii. (1891); Meschinelli and Sduinabol, Flora tertiaria italica (1892); this book contains a full bibliography relating to the Fossil Flora of Italy; J. S. Newberry, "The Flora of Amboy Clays," U.S. Geological Survey, Monograph xxvi. (1895); Hosius and von der Marck, " Die Flora der westphalischen Kreideformation," Palaeontographica, vol. xxvi. (188o), and supplement in ibid. vol. xxxi. (1883) ; A. G. Nathorst, " Glacialflora in Sachsen, am aussersten Rande des nordischen Diluviums," Kongl. Vetenskaps-Akad. Forh., p. 519 (1894) ; Clement Reid, " Pliocene Deposits of Britain," Mem. Geol. Survey (189o), Origin of the British Flora (1899); C. and E. M. Reid, " The Fossil Flora of Tegelen-sur-Meuse, near Venloo, in the Province of Limburg," Verh. Kon. Akad. Wetensch. Amsterdam, 2e Sect. DI. xiii. No. 6 (1907) ; " On the Pre-Glacial Flora of Britain," Journ. Linn. Soc. (Botany), xxxviii. 206-227 (1908); G. de Saporta, Prodrome dune flore fossile des Travertins anciens de Sezanne," Mem. soc. geol. France, 2nd series, vol. viii. p. 28? (1868); " Recherches sur les vegetaux fossiles de Meximieux, Archiv. Mus. hist. nat. Lyon, i. 131 (1876); Monde des plantes avant l'apparition de l'homme (1879) ; ' Etudes sur la vegetation du sud-est de la France a 1'epoque tertiare," Ann. sci. nat. (1862-1888); Flore fossile du Portugal (Lisbon, 1894) ; G. de Saporta and A. F. Marion, " Essai sur 1'etat de la vegetation a 1'epoque des marnes heersiennes de Gelinden," Mem. tour. acad. ray. belgique, vol. xxxvii. No. 6 (1873), and vol. xli. No. 3 (1878); J. Velenovsky, " Die Flora der bohmischen Kreideformation," in Beitrage zur Paleontologie Oesterreich-Ungarns and des Orients, vols. ii.-v. (1881-1885); Lester F. Ward, " Synopsis of the Flora of the Laramie Group," 6th Report U.S. Geological Survey, pp. 399-558 (1885) ; " The Geographical Distribution of Fossil Plants," 8th Report U.S. Geological Survey, pp. 663-96o (1889) ; " The Potomac Formation," 75th Report U.S. Geological Survey, pp. 307-398 (1895) ; " Some Analogies in the Lower Cretaceous of Europe and America," r6th Report U.S. Geological Survey, Pt. I., pp. 462-542 (1896) ; " The Cretaceous Formation of the Black Hills as indicated by the Fossil Plants," 79th Report U.S. Geological Survey, Pt. II., pp. 521-946 (1899). (C. R.)
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