XXVIII.—On the Geology of the South-east of Devonshire.

Abstract

Plates XLI., XLII. Introduction. The range of Dartmoor, independent of geological considerations, forms the most natural division of the county of Devon; and the following pages relate only to the southern portion, but which includes perhaps a greater number of distinct formations; presents them under circumstances more favourable for their study; and illustrates more points of geological interest than any other tract of equal extent in England. The object of the memoir is to describe, 1st, The several sedimentary formations; their mutual relations, and organic remains. 2nd, The igneous rocks. 3rd, General conditions; the amount of successive change and local disturbance. 1. Actual Period. (Map, Pl. XLI.) § 1. Estuary deposits .—Along the south coast of England, from the district where the older rocks first show themselves, all the rivers pour their waters into salt or brackish tidal estuaries, some of which are of considerable size; and it is necessary to notice them and certain points connected with such bodies of water, to enable the reader to appreciate the evidence from which we infer that the estuaries were at a former period more considerable, and that other valleys were once estuaries which have now ceased to be so. The rocks which bound the terminal valley of the Teign are, in the lower part, sandstones and conglomerates of the new red series; and, in the upper, inferior rocks; the length of the estuary being about five miles, but its breadth when full is