632 BEPOET— 1886. 



tively but about two inches thick, raises the questions, What can these conditions 

 have been? How was the pebble shifted in its ice or other matrix so that not 

 alone was one half of it subjected to the grinding process described, but (presum- 

 ably at another time) it. was turned completely over, and its directly opposite side, 

 even rnore perfectly smoothed and striated than any other, not to speak of the 

 remaining five surfaces, likewise ground and smoothed, though not as planes ? 



Supposing ice to have been the agent, what form would it have taken— shore 

 ice, floe ice, ground ice, floating or glacier ice ? 



SATURDAY, SEPTEMBER 4. 



The following Eeport and Papers were read : — 



1. Hei^ort on the Exploration of the Caves of North Wales. 

 See Reports, p. 219. 



2. On the Pleistocene Deposits of the Vale of Clwijd. 

 By Professor T. M'Kennt Hughes, M.A., F.G.S. 



The author cautions observers again? t inferring too hastilj'- the glacial origin of 

 beds from their containing glaciated boulders. He describes the older drifts of the 

 western part of North AVales, grouping them under two heads :— 



1. The Arenig Drift, or that in which boulders were transported from Snowdon 

 and Arenig into the Vale of Clwyd ; and 



2. The St. Asaph Drift, or that due to the destruction of tlie older glacial 

 deposits by marine action, during which boulders, which originally were carried on 

 ice from the north, and flints travelled in the shingle round the coast. Most of 

 the shells found in it are of species still living on the adjoining coast. A larger 

 proportion of the shells found in what he considers part of the same series of 

 deposits in neighbouring districts are of a Scandinavian or arctic type, and may 

 belong to an earlier part of the same age. 



He then gives an account of the principal caves explored about the Vale of 

 Clwyd, and explains their relation in each case to the drifts of the district ; inferring 

 that, while some of the caves themselves may be older than the marine Clwydian 

 drift, and some may possibly be even preglacial, yet that none of the bone-deposits 

 so far found in any of them can be referred to so early a date. 



3. Comparative Studies upon the Glaciation of North America, Great 

 Britain, and Ireland. By Professor H. Carvill Lewis, M.A., F.G.S. 



Observations extending over several years upon glacial phenomena on both sides 

 of the Atlantic had convinced the author of the essential identity of these phe- 

 nomena; and the object of this paper was to show that the glacial deposits of 

 Great_ Britain and Ireland, like those of America, may be interpreted most satis- 

 factorily by considering them with reference to a series of great terminal moraines, 

 which both define confluent lobes of ice and often mark the line separating the 

 glaciated from the non-glaciated areas. 



The paper began with a sketch of recent investigations upon the glaciation of 

 North America, with special reference to the significance of the terminal moraines 

 discovered within the last few years. The principal characters of these moraines 

 were given, and a map was exhibited showing the extent of the glaciated areas 

 of North America, the course of the interlobate and terminal moraines, and the 

 direction of striation and glacial movement. 



It was shown that, apart from the great ice-sheet of North-eastern America, 

 an immense lobe of ice descended from Alaska to Vancouver's Island on the 



