On the Supposed Pre-Cambrian Rocks of St. David's

Abstract

Introduction Some explanation is required of the grounds on which another contribution is added to the already voluminous literature connected with the rocks of St. David's. The circumstances under which I have reluctantly found myself compelled to make this contribution are briefly these. A new edition of the Rock Catalogue of the Museum of Practical Geology, Jermyn Street, being required, it became necessary to ascertain how far the stratigraphical order followed in previous editions required to be modified by the results of more recent research. In particular, the question of the existence of Pre-Cambrian rocks in Wales, which has emerged since the last issue of the Catalogue, appeared to demand full recognition in any republication of the work. I felt it to be due to those authors who have written so largely on this subject that ample acknowledgment of the results of their labours should be given. On the other hand, I was equally desirous that in admitting corrections of the views expressed upon the maps and sections of the Geological Survey I should do so from an actual inspection of the ground, which would enable me to judge how far and in what manner the required alterations should be made. It was obvious that in maps of districts surveyed forty years ago some important structures might have escaped notice, positive errors might have been committed, and petrographical details could not be expected to have been treated in a more satisfactory manner than in other English geological works of the same