368 D. MACKINTOSH ON HIGH-LEVEL MARINE DEIFTS. 



Braich) at a height of about 1450 feet above the sea (fig. 3), which 

 proved a submergence of the mountain to at least that extent. 



During a fourth visit to the Mountain-Lodge district (above 

 Euabon) I found that higher up than the extensive area of rounded 

 gravel there was an interval of angular detritus, above which (and 

 near to the summit of the mountain-range) at a height of about 

 1550 feet, there was a mass of gravel as much rounded as that in 

 which I found shells at a lower level. Gravel more or less rounded 

 reappeared on the west side of the mountain at nearly the same 

 height. 



During a third visit to Moel Tryfan (June 1881) I found that 

 several new sections had been exposed, in which a close inspection 

 showed that the edges of the slaty laminse were not continuously 

 curved, though the broken-off chips were arranged along more or 

 less curved lines which inclined from the jST.W. 



I ought to mention that, in the observations which have resulted 

 in this paper, I was again assisted by the Committee of the Govern- 

 ment Fund for Scientific Research. 



Discussion. 



The President, in inviting discussion, spoke of the great value of 

 Mr. Mackintosh's paper. 



Mr. DeRance spoke of the laborious manner in which Mr. 

 Mackintosh had carried out his work, and thought that he had done 

 much to refute the theory of a universal ice-cap overwhelming every 

 thing. He said that he had examined some of the Molluscan fragments 

 in Ireland, some of which were, indeed, scratched ; but others, he 

 thought, could only have been deposited during a submergence. He 

 thought that the positive evidence in favour of submergence must 

 overpower mere theory. As you ascend the slope of the Halkin 

 mountain from the river Dee, you pass first over Glacial Drift con- 

 taining erratics from the Lake district and south of Scotland ; in the 

 lower part a Boulder-clay resting on sands with Mollusca ; but higher 

 up the hill there is a different drift, local in character, and contain- 

 ing on]y North-Wales rocks. 



Mr. Ussher inquired if the Moel-Tryfan deposit abutted against 

 higher ground, as then the subaerial debris shed upon the beach 

 might have been mixed with it, and a local reversal of laminae pro- 

 duced by the impact of an iceberg. 



Prof. Bonnet said that he thought the facts brought forward by 

 Mr. Mackintosh would give a death-blow to the idea that the Mol- 

 lusca had been brought up hill by glaciers. He doubted, however, 

 whether the creep of the mingled sand and clays down hill would 

 not account for the bending of the slate-edges better than the 

 grounding of an iceberg ; for would not that bend them up hill? and 

 how would it ground on the lee side of the hill ? If terraces were 

 formed by the rising of the sea due to a polar ice-cap, then they 

 should not be uniform in level, but rise along circles of longitude 

 towards the pole. 



