On the Monian System of Rocks

Introduction. Is there no order in Pre-Cambrian rocks? Do they consist in one area of great undulating masses of gneiss, in which those who have studied them refuse to recognize any stratigraphical sequence, and in another of tiny fragments of formations, two or three of which may be contained within an area of a few square miles ? and are these types in no way connected ? Such were the questions which forced themselves upon me after brief consecutive visits to the Highlands and St. David's. Consulting my friend Dr. Callaway on these points, he advised me to go to Anglesey, where I should find rocks that might fairly be compared with the gneiss of the Highlands in character, in close proximity to, if not associated with, volcanic rocks of the type of St. David's. I went; and after three years' work in summer and spring vacations have arrived at conclusions which I now venture to lay before the Society. But in the forefront of this inquiry we are met by the fact that Sir Andrew Ramsay, who knows the district as one knows one's native hills, has declared that there are no Pre-Cambrian rocks in Anglesey at all. Can we ignore this fact? or must we not first ascertain the reasons which have led to this conclusion ? If after a study of the area, sufficiently prolonged to place one's self somewhat on a level with his knowledge of the rocks, one reads his words, they strike one as