On the Older Rocks of South Devon and East Cornwall

Abstract

I n the course of last year I made an examination of the older rocks of South Devon and the adjacent portions of Cornwall, for the purpose of ascertaining the stratigraphical relations of the different beds, or groups of beds, with a view to their coordination with the more complete and better-known series in the northern part of the county. I was led to undertake this in the belief that, notwithstanding the many memoirs that have appeared on Devonian Geology, there was still a very great difference of opinion among geologists respecting the relations of the beds on the south side of the Calm-measures; and any one who is acquainted with the literature of the subject will, I think, admit the fact. Indeed the late Sir Henry De la Beche, subsequently to his last essay in the first volume of the Memoirs of the Geological Survey, regarded the succession of the rocks as still unravelled, and expressed his intention of taking an early opportunity of revising this portion of his labours*. Many of the difficulties which stood in the way of the pioneers of Devonian geology have long since been cleared away, more especially by the publication of the Geological Survey-maps of Devon and Cornwall, the general accuracy of which is all the more remarkable as it was the first attempt at anything in equal detail in this country; and a great step was made towards a better understanding of the structure of the Devonian country when Prof. Sedgwick and Sir