On the Cambrian and associated Rocks in North-west Caernarvonshire

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Abstract
Introduction. The area to which the present memoir refers has for a long time attracted the attention of geologists, partly because within it may be found the oldest portion of the Cambrian series, and therefore the supposed base of our known stratified rocks, and partly because, of late years, there has been an expectation of finding here some representatives of still older series. The most recent observers, indeed, agree in regarding the whole of the mass coloured as porphyry between Bangor and Caernarvon, and some part of that coloured altered Cambrian, as belonging to a Pre-Cambrian epoch, and the felsite of Llyn Padarn and Moel Tryfaen they treat in the same way. There is no difference of opinion between them on this latter area, but as to the former, though all divide the mass into three parts—the mass near Caernarvon, the mass near Dinorwic, and that near Bangor,—Prof. Hughes considers all three a connected series of “beds,” Prof. Bonney regards the Caernarvon rock as very old, and the other two as connected, while Dr. Hicks regards them as representing three independent and unconformable groups. Again, Prof. Bonney and Prof. Hughes differ as to the stratigraphy near Bangor, with the effect that the former considers much more to be Pre-Cambrian than the latter does. All three views are diametrically opposed to that of the Survey, not only as to theories but as to many of the facts. Nor has the Survey given way. Prof. Ramsay, in 1881*, says the proposed changes

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