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SECTION IN CENTRAL

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Originally appearing in Volume V27, Page 641 of the 1911 Encyclopedia Britannica.
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SECTION IN CENTRAL  See also:WASHINGTON 250 ft . 4000 ft . . 3500 ft . . C . 3000 ft . . 4000 „ . 0–2000 „ winds also are much affected by the changes of pressure due to the strong See also:continental changes of temperature . The warmed See also:air of summer produces an See also:area of See also:low pressure in the See also:west-central See also:United States, which interrupts the See also:belt of high pressure that planetary conditions alone would See also:form around the See also:earth about See also:latitude 300; hence there is a tendency of the summer winds to See also:blow inward from the See also:northern Pacific over the Cordilleras toward the continental centre, and from the trades of the torrid See also:Atlantic up the See also:Mississippi Valley; conversely in See also:winter See also:time, the See also:cold air over the lands produces a large area of high pressure from which the winds tend to flow outward; thus repelling the See also:westerly winds of the northern Pacific and greatly intensifying the outflow southward to the Gulf of See also:Mexico and eastward to the Atlantic . As a result of these seasonal alternations of temperature and pressure there is something of a See also:monsoon tendency See also:developed in the winds of the Mississippi Valley, southerly inflowing winds prevailing in summer and northerly outflowing winds in winter; but the See also:general tendency to inflow and outflow is greatly modified by the See also:relief of the lands, to which we next turn . The See also:climatic effects of relief are seen directly in the ascent of the higher See also:mountain ranges to altitudes where low temperatures prevail, thus preserving See also:snow patches through the summer on the high summits (over rz,000 ft.) in the See also:south, and maintaining snow-See also:fields and moderate-sized glaciers on the ranges in the See also:north . With this goes a general increase of precipitation with See also:altitude, so that a See also:good rainfall See also:map would have its darker shades very generally along the mountain ranges . Thus the heaviest measured rainfall See also:east of the Mississippi is on the See also:southern Appalachians; while in the west, where observations are as yet few at high level stations, the occurrence of forests and pastures on the higher slopes of mountains which rise from See also:desert plains clearly testifies to the same See also:rule .

The mountains also introduce controls over the See also:

local winds; diurnal warming in summer suffices to cause local ascending breezes which frequently become cloudy by the expansion of ascent, even to the point of forming local See also:thunder showers which See also:drift away as they grow and soon dissolve after leaving the See also:parent mountain . Conversely, nocturnal cooling produces well-defined descending breezes which issue from the valley mouths, sometimes attaining an unpleasant strength toward midnight . The mountains are of larger importance in obstructing and deflecting the course of the general winds . The Pacific ranges, See also:standing transverse to the course of the prevailing westerlies near the Pacific Ocean, are of the greatest importance in this respect; it is largely by See also:reason of the barrier that they form that the tempering effects of the Pacific winds are See also:felt for so See also:short a distance inland in winter, and that the See also:heat centre is displaced in summer so far towards the western See also:coast . The rainfall from the stromy westerly winds is largely deposited on the western slopes of the mountains near the Pacific coast, and arid or desert interior plains are thus found See also:close to the See also:great ocean . The descending winds on the eastern slopes of the ranges are frequently warm and dry, to the point of resembling the See also:Fohn winds of the See also:Alps; such winds are known in the Cordilleran region as See also:Chinook winds . The ranges of the Rocky Mountains in their turn receive some rainfall from the passing winds, but it is only after the westerlies are reinforced by a moist indraft from the Gulf of Mexico and the Atlantic—the result of summer or of cyclonic inflow—that rainfall increases to a sufficient measure on the See also:lower lands to support See also:agriculture without See also:irrigation . The region east of the Mississippi is singularly favoured in this way; for it receives a good amount of rainfall, well distributed through the See also:year, and indeed is in this respect one of the largest regions in the temperate zones that are so well watered . The Great Plains are under correspondingly unfavourable conditions, for their scanty rainfall is of very variable amount . Along the transition belt between plains and prairies the See also:climate is peculiarly trying as to rainfall ; one See also:series of five or ten years may have sufficient rainfall to enable the farmers to gather good crops; but the next series following may be so dry that the crops fail year after year . The cyclonic inflows and anticyclonic outflows, so characteristic of the belt of westerly winds the See also:world over, are very irregular in the See also:Cord illeran region; but farther eastward they are typically developed by reason of the great extent of open See also:country . Although of reduced strength in the summer, they still suffice to dominate See also:weather changes; it is during the approach of a low pressure centre that hot southerly winds prevail; they sometimes reach so high a temperature as to See also:wither and blight the See also:grain crops; and it is almost exclusively in connexion with the cloudy areas near and south-east of these cyclonic centres that violent thunderstorms, with their occasional destructive whirling tornadoes, are formed .

With the passing of the low pressure centre, the winds shift to west or north-west, the temperature falls, and all nature is relieved . In winter-time, the cyclonic and anticyclonic areas are of increased frequency and intensity; and it is partly for this reason that many meteorologists have been disposed to regard them as chiefly driven by the irregular flow of the westerly winds, rather than as due to convectional instability, which should have a maximum effect in summer . One of the best indications of actual winter weather, as apart from the arrival of winter by the See also:

calendar, is the development of cyclonic disturbances of such strength that the See also:change from their warm, See also:sirocco-like southerly inflow hi front of theircentre, to the " cold See also:wave " of their See also:rear produces non-periodic temperature changes strong enough to overcome the weakened diurnal temperature changes of the cold See also:season, a relation which practically never occurs in summer time . A curious feature of the cyclonic storms is that, whether they See also:cross the interior of the country near the northern or southern boundary or along an intermediate path, they converge towards New See also:England as they pass on toward the Atlantic ; and hence that the north-eastern See also:part of the United States is subjected to especially numerous and strong weather changes . (W . M . D.) IV.—See also:FAUNA AND See also:FLORA Fauna.—See also:Differences of temperature have produced in North See also:America seven transcontinental See also:life-zones or areas characterized by relative uniformity of both fauna and flora; they are the See also:Arctic, Hudsonian and See also:Canadian, which are divisions of the Boreal Region; the Transition, Upper Austral and Lower Austral, which are divisions of the Austral Region, and the Tropical . The Arctic, Hudsonian and Canadian enter the United States from the north and the Tropical from the south; but the greater part of the United States is occupied by the Transition, Upper Austral and Lower Austral, and each of these is divided into eastern and western subzones by differences in the amount of moisture . The Arctic or Arctic-Alpine See also:zone covers in the United States only the tops of a few mountains which extend above the limit of trees, such as Mt Katandin in See also:Maine, Mt Washington and neighbouring peaks in the See also:White Mountains of New See also:Hampshire, and the loftier peaks of the Rocky, Cascade and Sierra See also:Nevada Mountains . The larger animals are rare on these mountain-tops and the areas are too small for a distinct fauna . The Hudsonian zone covers the upper slopes of the higher mountains of New England, New See also:York and North Carolina and larger areas on the elevated slopes of the Rocky and Cascade Mountains; and on the western mountains it is the See also:home of the mountain See also:goat, mountain See also:sheep, Alpine flying-See also:squirrel, See also:nutcracker, evening See also:grosbeak and Townsend's See also:solitaire . The Canadian zone crosses from See also:Canada into northern and north-western Maine, northern and central New Hampshire, northern See also:Michigan, and north-eastern See also:Minnesota and North Dakota, covers the See also:Green Mountains, most of the See also:Adirondacks and Catskills, the higher slopes of the mountains in See also:Pennsylvania, West See also:Virginia, Virginia, western North Carolina and eastern See also:Tennessee, the lower slopes of the northern Rocky and Cascade Mountains, the upper slopes of the southern Rocky and Sierra Nevada Mountains, and a See also:strip along the Pacific coast as far south as Cape Mendocino, interrupted, however, by the See also:Columbia Valley .

Among its characteristic mammals and birds are the See also:

lynx, See also:marten, See also:porcupine, northern red squirrel, Belding's and See also:Kennicott's ground squirrels, varying and snowshoe rabbits, northern See also:jumping See also:mouse, white-throated See also:sparrow, Blackburnian See also:warbler, See also:Audubon warbler, See also:olive-backed See also:thrush, three-toed See also:woodpecker, spruce See also:grouse, and Canada See also:jay; within this zone in the North-eastern states are a few See also:moose and caribou, but farther north these animals are more characteristic of the Hudsonian zone . The Transition zone, in which the extreme southern limit of several boreal See also:species overlaps the extreme northern limit of numerous austral species, is divided into an eastern humid or Alleghanian area, a western arid area, and a Pacific coast humid area . The Alleghanian area comprises most of the lowlands of New England . New York and Pennsylvania, the north-east corner of See also:Ohio, most of the lower See also:peninsula of Michigan, nearly all of See also:Wisconsin, more than See also:half of Minnesota, eastern North Dakota, north-eastern South Dakota, and the greater part of the Appalachian Mountains from Pennsylvania to See also:Georgia . It has few distinctive species, but within its See also:borders the southern See also:mole and See also:cotton-tail See also:rabbit of the South meet the northern See also:star-nosed and See also:Brewer's moles and the varying See also:hare of the North, and the southern bobwhite, See also:Baltimore See also:oriole, bluebird, catbird, chewink, thrasher and See also:wood thrush are neighbours of the bobolink, solitary vireo and the See also:hermit and See also:Wilson s thrushes . The Arid Transition life-zone comprises the western part of the Dakotas, north-eastern See also:Montana, and irregular areas in Washington, See also:Oregon, See also:Idaho, See also:Wyoming, See also:California, Nevada, See also:Utah, See also:Colorado, See also:Arizona, New Mexico and western See also:Texas, covering for the most part the eastern See also:base of the Cascade and Sierra Nevada Mountains and the higher parts of the Great See also:Basin and the plateaus . Its most characteristic animals and birds are the white-tailed See also:jack-rabbit, pallid See also:vole, See also:sage See also:hen, See also:sharp-tailed grouse and green-tailed towhee; the large Columbia ground-squirrel (Spermophilus columbianus) is See also:common in that part of the zone which is west of the Rocky Mountains, but east of the Rockies it is replaced by another species (Cynomys) which closely resembles a small See also:prairie See also:dog . The Pacific Coast Transition life-zone comprises the region between the Cascade and Coast ranges in Washington and Oregon, parts of northern California, and most of the California coast region from Cape Mendocino to See also:Santa See also:Barbara . It is the home of the Columbia See also:black-tail See also:deer, western See also:raccoon, Oregon spotted See also:skunk, See also:Douglas red squirrel, Townsend's chipmunk, tailless sewellel (Haplodon See also:rufus), See also:peculiar species of See also:pocket gophers and voles, Pacific coast forms of the great-horned, spotted, screech and pigmy owls, sooty grouse, Oregon ruffed grouse, Steller's jay, See also:chestnut-backed chickadee and Pacific winter See also:wren . The Upper Austral 634 zone is divided into an eastern humid (or Carolinian) area and a western arid (or Upper Sonoran) area . The Carolinian area ex-tends from southern Michigan to northern Georgia and from the Atlantic coast to western See also:Kansas, comprising See also:Delaware, all of See also:Maryland except the mountainous western portion, all of Ohio except the north-east corner, nearly the whole of See also:Indiana, See also:Illinois, See also:Iowa and See also:Missouri, eastern See also:Nebraska and Kansas, south-eastern South Dakota, western central See also:Oklahoma, northern See also:Arkansas, See also:middle and eastern See also:Kentucky, middle Tennessee and the Tennessee valley in eastern Tennessee, middle Virginia and North Carolina, western West Virginia, north-eastern See also:Alabama, northern Georgia, western South Carolina, the See also:Connecticut Valley in Connecticut, the lower See also:Hudson Valley and the See also:Erie basin in New York, and narrow belts along the southern and western borders of the lower peninsula of Michigan . It is the northernmost home of the See also:opossum, See also:grey See also:fox, fox squirrel, See also:cardinal See also:bird, Carolina wren, tufted tit, See also:gnat catcher, summer See also:tanager and yellow-breasted chat .

The Upper Sonoran life-zone comprises south-eastern Montana, central, eastern and north-eastern Wyoming, a portion of south-western South Dakota, western Nebraska and Kansas, the western extremity of Oklahoma, north-western Texas, eastern Colorado, south-eastern New Mexico, the Snake plains in Idaho, the Columbia plains in Washington, the Malheur and Harney plains in Oregon, the Great See also:

Salt See also:Lake and See also:Sevier deserts in Utah, and narrow belts in California, Nevada and Arizona . Among its characteristic mammals and birds are the sage cotton-tail, black-tailed jack-rabbit, Idaho rabbit, Oregon, Utah and Townsend's ground squirrels, sage chipmunk, five-toed See also:kangaroo rats, pocket mice, See also:grasshopper mice, burrowing See also:owl, Brewer's sparrow, Nevada sage sparrow, lazuli See also:finch, sage thrasher, See also:Nuttall's poor-will, See also:Bullock's oriole and rough-winged See also:swallow . The Lower Austral zone occupies the greater part of the Southern states, and is divided near the 98th See also:meridian into an eastern humid or Austroriparian area and a western arid or Lower Sonoran area . The Austroriparian zone comprises nearly all the Gulf States as far west as the mouth of the Rio Grande, the greater part of Georgia, eastern South Carolina, North Carolina and Virginia, and extends up the lowlands of the Mississippi Valley across western Tennessee and Kentucky into southern Illinois and-Indiana and across eastern and southern Arkansas and eastern Oklahoma into south-eastern Missouri and Kansas . It is the home of the southern fox-squirrel, cotton See also:rat, ricefield rat, wood rat, See also:free-tailed See also:bat, mocking bird, painted See also:bunting, prothonotary warbler, red-cockaded woodpecker, chuckwill's-widow, and the swallow-tailed and Mississippi kites . A southern portion of this zone, comprising a narrow strip along the Gulf Coast from Texas to See also:Florida and up the Atlantic coast to South Carolina, is semi-tropical, and is the northernmost habitation of several small mammals, the See also:alligator (Alligator mississippiensis), the ground See also:dove, white-tailed See also:kite, Florida screech owl and See also:Chap-See also:man s See also:night-See also:hawk . The Lower Sonoran zone comprises the most arid parts of the United States: south-western Texas, south-western Arizona and a portion of northern Arizona, southern Nevada and a large part of southern California . Some of its characteristic mammals and birds are the See also:long-eared desert fox, four-toed kangaroo rats, Sonoran pocket mice, big-eared and tiny white-haired bats, road runner, See also:cactus wren, See also:canyon wren, desert thrashers, hooded oriole, black-throated desert sparrow, Texas night-hawk and Gambel's See also:quail . It is the northernmost home of the See also:armadillo, See also:ocelot, See also:jaguar, red and grey See also:cats, and the spiny pocket mouse, and in southern Texas especially it is visited by several species of tropical birds . There is some resemblance to the Tropical life-zone at the south-eastern extremity of Texas, but this zone in the United States is properly restricted to southern Florida and the lower valley of the Colorado along the border of California and Arizona, and the knowledge of the latter is very imperfect . The area in Florida is too small for characteristic tropical mammals, but it has the true See also:crocodile (Crocodilus americanus) and is the home of a few tropical birds . Most of the larger See also:American mammals are not restricted to any one faunal zone .

The bison, although now nearly See also:

extinct, formerly roamed over nearly the entire region between the Appalachian and the Rocky Mountains . The black See also:bear and See also:beaver were also widely distributed . The Virginia deer still ranges from Maine to the Gulf states and from the Atlantic coast to the Rocky Mountains . The grizzly bear, cougar, See also:coyote, prairie dog and See also:antelope are still found in several of the Western states, and the grey See also:wolf is common in the West and in northern Minnesota, Wisconsin and Michigan . Flora.—The Alpine flora, which is found in the United States only on the tops of those mountains which rise above the limit of trees, consists principally of a variety of See also:plants which See also:bloom as soon as the snow melts and for a short season make a brilliant display of See also:colours . The flora of the Hudsonian and the Canadian zone consists largely of white and black spruce, tamarack, See also:canoe-See also:birch, See also:balsam-See also:poplar, balsam-See also:fir, See also:aspen and grey See also:pine . In the Alleghanian Transition zone the chestnut, See also:walnut, oaks and hickories of the South are interspersed among the See also:beech, birch, See also:hemlock and See also:sugar See also:maple of the North . In the Western Arid Transition zone the flora consists largely of the true sage See also:brush (See also:Artemisia tridentala), but some tracts are covered with forests of yellow or See also:bull pine (Pinus ponderosa) . The Pacific coast Transition zone is noted for its forests of See also:giant[See also:POPULATION conifers, principally Douglas fir, See also:Sitka spruce, Pacific See also:cedar and Western hemlock . Here, too, mosses and ferns grow in profusion, and the sadal (Gaultheria shallon), See also:thimble See also:berry (Rubus nootkamus), See also:salmon berry (Rubus spectabilis) and See also:devil's See also:club . (Fatsia horrida) are characteristic shrubs . In the Carolinian zone the See also:tulip See also:tree, sycamore, sweet See also:gum, See also:rose See also:magnolia, short-See also:leaf pine and sassafras find their northernmost limit Sage brush is common to both the western arid Transition zone and the Upper Sonoran zone, but in suitable soils of the latter several greasewoods (Artiplex confertifolia, A. canescens, A. nuttalli, Tetradymia canescens, Sarcobatus vermicuiatus and Grayia spinosa) are characteristic species, and on the mountain slopes are some See also:nut pines (piiion) and junipers .

The Austroriparian zone has the long-leaf and loblolly pines, magnolia and live See also:

oak on the uplands, and the bald See also:cypress, tupelo and See also:cane in the swamps; and in the semi-tropical Gulf' trip are the See also:cabbage See also:palmetto and Cuban pine; here, too, See also:Sea See also:Island cotton and tropical fruits are successfully cultivated . The Lower Sonoran zone is noted for its cactuses, of which there is a great variety, and some of them grow to the height of trees; the See also:mesquite is also very large, and the See also:creosote See also:bush, acacias, yuccas and agaves are common . The Tropical belt of southern Florida has the royal See also:palm. coco-nut palm, See also:banana, See also:Jamaica See also:dogwood, manchineel and See also:mangrove; the Tropical belt in the lower valley of the Colorado has giant cactuses. desert acacias, palo-verdes and the Washington or See also:fan-leaf palm . Almost all of the United States east of the 98th meridian is naturally a See also:forest region, and forests See also:cover the greater part of the Rocky Mountains, the Cascades, the Sierra Nevadas and the Coast Range, but throughout the belt of plains, basins and deserts west of the Rocky Mountains and on the Great Plains east of the Rocky Mountains there are few trees except along the watercourses, and the prevailing type of vegetation ranges from bunch grass to sage brush and cactuses according to the degree of aridity and the temperature . In the eastern forest region the number of species decreases somewhat from south to north, but the entire region differs from the densely forested region of the Pacific Coast Transition zone in that it is essentially a region of See also:deciduous or hardwood forests, while the latter is essentially one of coniferous trees; it differs from the forested region of the Rocky Mountains in that the latter is not only essentially a region of coniferous trees, but one where the forests do not by any means occupy the whole area, neither do they approach in See also:density or economic importance those of the eastern See also:division of the country . Again, the forests of most of the eastern region embrace a variety of species, which, as a rule, are very much intermingled, and do not, unless quite exceptionally, occupy areas chiefly devoted to one species ; while, on the other See also:hand, the forests of the west—including both Rocky Mountain and Pacific coast divisions—exhibit a small number of species, considering the vast area embraced in the region; and these species, in a number of instances, are extraordinarily limited in their range, although there are cases in which one or two species have almost exclusive See also:possession of extensive areas . V.—POPULATION AND SOCIAL CONDITIONS See also:Geographical Growth of the Nation.—The achievement of See also:independence found the See also:people of the United States owning the entire country between the Gulf and the Great Lakes, excepting only Florida, as far to the west as the Mississippi; but the actual settlements were, with a few See also:minor exceptions, confined to a strip of territory along the Atlantic See also:shore . The See also:depth of See also:settlement, from the coast inland, varied greatly, ranging from what would be involved in the See also:mere occupation of the shore for fishing purposes to a See also:body of agricultural occupation extending back to the base of the great Atlantic See also:chain, and averaged some 250 M .l Westward, beyonc the general See also:line of continuous settlement, i In the Statistical See also:Atlas See also:volume of the See also:census of 1900 the reader will find for each decennial census since 1790 a map showing the See also:distribution of population, w'th indication of the density of settlement, and an elaborate explanatory See also:text . In Orin See also:Grant Libby's Geographical Distribution of the See also:Vote of the Thirteen States on the Federal Constitution, 1787–1788 (University of Wisconsin, See also:Madison, 1894), along ,with a valuable map interesting facts are given regarding the social and economic characteristics of different sections . were four extensions of population through as many gaps in ; See also:Ito years moved more than 500 m westward, almost exactly the Appalachian barrier, constituting the four See also:main paths along the 39th parallel of latitude: 9.5 degrees of See also:longitude, along which See also:migration westward first took See also:place: the See also:Mohawk Valley in New York, the upper See also:Potomac, the Appalachian Valley, and around the southern base of the Appalachian See also:system . Four outlying See also:groups beyond the mountains, with perhaps a twentieth part of the See also:total population of the nation, -one about See also:Pittsburg, one in West Virginia, another in northern Kentucky, and the last in Tennessee: all determined in situation by See also:river highways-See also:bore See also:witness to the qualities of strength and courage of the American See also:pioneer . Finally, there were in 1790 about a See also:score of small trading or military posts, mainly of See also:French origin, scattered over the then almost unbroken See also:wilderness of the upper Mississippi Valley and region of the Great Lakes .

Twelve decennial censuses taken since that time (1800-191o) have revealed the extraordinary spread of population over the See also:

present area of the country (see CENSUS : United States) . The large percentage of the population, particularly Continental United States, exclusive of See also:Alaska . Population enumerated . Areas (excluding See also:water), in square See also: