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DALRADIAN

Online Encyclopedia
Originally appearing in Volume V07, Page 777 of the 1911 Encyclopedia Britannica.
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DALRADIAN, in geology, a series of metamorphic rocks, typically developed in the high ground which lies E. and S. of the Great Glen of Scotland. This was the old Celtic region of Dalradia, and in 1891 Sir A. Geikie proposed the name Dalradian as a convenient provisional designation for the complicated set of rocks to which it is difficult to assign a definite position in the stratigraphical sequence (Q.J.G.S. 47, p. 75): In Sir A. Geikie's words, " they consist in large proportion of altered sedimentary strata, now found in the form of mica-schist, graphite-schist, andalusite-schist, phyllite, schistose grit, greywacke and conglomerate, quartzite, limestone and other rocks, together with epidiorites, chlorite-schists, hornblende schists and other allied varieties, which probably mark sills, Sava-sheets or beds of tuff, intercalated among the sediments. The total thickness of this assemblage of rocks must be many thousand feet." The Dalradian series includes the " Eastern or Younger schists " of eastern Sutherland, Ross-shire and Inverness-shire—the Moine gneiss, &c.—as well as the metamorphosed sedimentary and eruptive rocks of the central, eastern and south-western Highlands. The series has been traced into the north-western counties of Ireland. The whole of the Dalradian complex has suffered intense crushing and thrusting. See PRE-CAMBRIAN; also J. B. Hill, Q.J.G.S., 1899, 55, and G. Barrow, loc. cit., 1901, 57, and the Annual Reports and Summaries of Progress of the Geological Survey of the United Kingdom from 1893 onwards.
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