112 PEOF. T. X'KEX>'Y HrGHES 



11. Oil ilie Cae Gwt2s' Cave. By T. :5J:'=Kbkst Hughes, :Sl.A., 

 P.G.S., Woodwardian Professor of Geology, Cambridge. (Eead 

 Js'ovember 23, 1887.) 



l:s a communication which I made to the Society '^ On the Drifts of 

 the Yale of Clwyd and their Eelation to the Caves and Cave- 

 deposits ''*, I considered the subject under the following heads: — 



(1) The Age of the Drift. 



(2) The Eelation of the Deposits in the Caves to that Drift. 



In discussing the age of the drift, I -was of course obliged to 

 offer a tentative classification of the Pleistocene deposits of the 

 district, in order to show the relative position and age of the St. 

 Asaph beds, to which I referred the drift on the flanks of the hill in 

 which the Pfynnon Beuno Caves occur. 



The classification I suggested has been called in question, and I 

 have relegated the discussion of this part of the subject in its wider 

 bearing to a separate paper. 



It will be desirable, however, to restate briefly the conclusions at 

 which I then arrived. They were : — 



That the interpretation of the glacial phenomena of Xorth Wales 

 is much more simple than that suggested by most recent observers 

 in East England. 



That we have evidence of the following sequence of events : — 



That glacier-ice came down from the Snowdon and Arenig group 

 of mountains, riding across pre-existing north and south valleys as 

 far at any rate as the Cheshire plain on the east, and as far as the 

 Irish Channel, which was the corresponding north and south valley 

 on the west. 



That glacier-ice came also from the north and held back the 

 "Welsh ice along the whole of the north coast ; that it once sent a 

 tongue further down the Irish Sea and. perhaps, another down the 

 east side of Wales towards the " Severn Straits " ; that this north- 

 country ice was melted back when the Welsh ice was receding, so 

 that it never left any moraine matter far south of the coast-line. 



That there may have been interruptions in the movements, but 

 that there is no evidence of any interglacial age. 



■niat there was a submergence of the mountain lands, southern 

 Mollusca coming in as the sea advanced and the glaciers were 

 melted into the recesses of the Welsh mountains, and the more 

 northern forms following the ice as it receded to the north. 



That there was a great denudation of the old glacial deposits and a 

 using up of the morainic deposits of both northern and western ice 

 along their ancient line of contact. 



That there was never again any ice action in the Yale of Clw^'d 

 different from what may be seen at the present time in the estuary 

 of the Dee. 



* Quart. Joum. Geol. Soc. 1886, toL xliii. p. 73. 



