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Excerpt from The Geology of the Country Around, Plymouth Liskeard The original geological survey of this area by De la Beche was published during the years 1834 and 1835, almost wholly on Sheets 24 and 25 of the old series one-inch maps. These sheets were revised in 1839, when the "Carbonaceous series" was separated from the "Grauwacke series"; and about the year 1846 (or 1845) the classification and colouring were modified. Do la Beche then adopted the term Devonian Rocks, and stated on the index of colours that they were represented by "A provisional colour, as there is reason to consider that the rocks included under this bead in Cornwall and Devon are equivalents of Carboniferous Limestone, Old lied Sandstone, and Upper Silurian Rocks." The igneous rocks and the Devonian limestones were separated from the mass of slates and grits on De la Beche's map, but the succession of the rock-groups, and the intimate structure of the area had not been determined. In his monumental 'Report on the Geology of Cornwall, Devon and West Somerset, ' published in 1839, De la Beche described the leading types of rock, and made many suggestions with regard to their correlation that have not stood the test of later detailed researches. Nevertheless, his facts were noted with such precision that the present author, from experience he had gained in the Devonian area of South Devon, was enabled so to interpret De la Beebe's observations as to be able to give in 1890 a forecast of the probable structure in the Devonian rocks of Cornwall. Mr. Ussher then represented on a small man of that county the equivalents of the main divisions which with great care and labour ho had established in Devonshire. It is interesting to find that the great structural feature in the Plymouth area, the faulting that displaces the Lower Devonian rocks and brings them for some distance against Upper Devonian, was depicted on that map of 1890, and that the main sub-divisions, which Mr. Ussher has established in Devonshire, have been confirmed by the detailed work since carried out by the Geological Survey. The area represented by this map was surveyed on the six-inch scale by Mr. Ussher, who has also written the memoir. The petrology of the igneous rocks has been dealt with by Dr. J. S. Flett, and Mr. D. A. MacAlister has contributed particulars relating to mines and minerals. The author of the memoir has given an historical account of the progress of geological knowledge in the area, and he has also compiled a bibliography which is printed as an appendix. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.