102 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 1 894, 



ground, such as might yield a fauna. Hence there is little to be 

 hoped from the possible discovery of fossils. So long, therefore, as 

 the matter has to be decided by stratigraphy, aided sometimes by 

 lithological considerations, the fight is apt to be prolonged. 



Now, as regards the latter method, Prof. Bonney, we are told, 

 has often insisted on the slight degree of difference between some of 

 the later Pebidian and the earlier Cambrian rocks. This is the view 

 that I have myself always maintained with regard to the beds in South 

 Wales. Consequently, where palaeontology, as at present, gives us 

 no clue and where lithological distinctions fail, if we wish to draw 

 a line at all we are bound to fall back on stratigraphy. It rests, 

 then, with those who are desirous of establishing the existence of 

 pre-Cambrian rocks in North-west Caernarvonshire to draw that line. 

 Do they still believe in the existence of a basal Cambrian conglome- 

 rate along the eastern margin of the great felsite mass which 

 terminates at Llanllyfni ? Prof. Blake alleges that conglomerates 

 and felsites are apt to wait upon each other without special refer- 

 ence to period, while Dr. Hicks but lately spoke of a pre-Cambrian 

 ridge in the neighbourhood of the Penrhyn slate-quarries, on both 

 sides of which the Cambrian succession is shown, the basal Cambrian 

 conglomerate being traceable on an irregular pre-Cambrian floor. 

 At this stage the controversy rests for the present. If an impartial 

 jury were empannelled and the evidence now available placed before 

 them, it is probable that they would take refuge from their perplexity 

 in a verdict of ' Not Proven ' to each of the various contentions. 



To this subdivision of the Fundamental Rocks also belongs Prof. 

 Lloyd Morgan's paper on the Pebidian volcanic series of St. David's, 

 which, for reasons already mentioned, I am precluded from noticing 

 on the present occasion. The clastic rocks of Charnwood Forest, 

 too, as decided in their recent paper by Messrs. Hill and Bonney, 

 are likewise referred to the latest epoch in. the pre-Cambrian series — 

 the Pebidian. 



The Crystalline Schists, etc. — The term Archaean is by some 

 restricted to the lower subdivision of the Fundamental Rocks. Be 

 this as it may, the Crystalline Schists and Gneisses are sufficiently 

 distinct from the rocks of the upper subdivision to be considered 

 under a separate section. Again, then, we seem bound to turn to 

 Messrs. Peach and Home's exhaustive memoir for an account not 

 only of the original types of Lewisian Gneiss, but also of the 

 subsequent changes which these have undergone. This subject has, 



