On an Unconformable Break at the Base of the Cambrian Rocks near Llanberris

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Abstract
T he short paper which I have to lay before the Society has been suggested by several previous communications on the subject of rocks older than, and unconformable to, the Cambrian Slates of North Wales. In the year 1867 I brought before the British Association at the Dundee meeting the accompanying section on the Llanberris and Carnarvon Railway, then for the first time exposed in a new cutting near Llanberris. The section was subsequently published in the ‘Geological Magazine’ for March 1868, to which I must refer the reader. Up to this time no suspicion existed of the occurrence of an unconformable series of ancient rocks in North Wales older than the Cambrians. Previous to this the researches of Dr. Hicks in Pembrokeshire established in that district the fact of the occurrence of great series of beds unconformable to the overlying Cambrians; but during the succeeding seven or eight years no fresh observations were made in the Llanberris district. At the reading of Dr. Hicks's paper on December 2, 1874, I pointed out an apparent analogy between the Pembrokeshire series and that at Llanberris; and this, I believe, induced Professor Hughes and Dr. Hicks to visit Llanberris, and their observations on that district were recently communicated to the Society (Q. J. G. S. vol. xxxiv. pp. 137 & 147). Rather singularly, they disagree with me in the conclusion 1 arrived at, that there was a visible break in the series of rocks exposed in the Llanberris railway-cutting, but admit that such

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