D. MACKINTOSH ON THE CEPN AND PONT-NEWYDD CAVE-DEPOSITS. 93 



The stalagmitic crust (3) must have been accumulated during a 

 period when conditions were favourable ; and these conditions must 

 have varied in different parts of the Cefn cave. 



The bed under the stalagmite in the Cefn cave, with its repre- 

 sentative in the Pont-new3 ;r dd cave, is the most difficult to explain. 

 I am unable to say whether it most resembles an accumulation of 

 fine river-shingle or a raised beach. In the caves it does not occur 

 at the height above the present sea-level of the more typical raised 

 beaches. It is not confined to the caves, but may be seen at inter- 

 vals along the sloping north bank of the Elwy. It may likewise be 

 found in patches along the Elwy valley as far as the Vale of Clwyd, 

 where it would appear to graduato into the middle gravel and sand 

 which underlies the upper clay. However it may have originated, 

 I cannot believe with Professor Hughes that, in the Pont-newydd 

 cave, it was washed in through a swallow-hole, from the Boulder- 

 clay of the neighbourhood, by a freshwater stream. The relative 

 proportion of stones of different kinds is not nearly the same in the 

 pebble-bed and in the Boulder-clay covering the surface of the 

 ground at a higher level. In the pebble-bed nearly all the stones, 

 so far as I could see, are Denbighshire sandstone or grit. In the 

 Boulder-clay a large proportion of the pebbles are limestone. I 

 could only see one felstone specimen in the pebble-bed (though 

 others probably might be found). In the Boulder-clay felstone 

 pebbles and boulders are far from being rare *. The pebble-bed is 

 not confined to the cavern or the ground straight in front of it, as it 

 would have been if deposited by a stream flowing out of the cavern ; 

 but it may be seen in a recess a short distance east of the mouth of 

 the cavern, and, as I have already remarked, at intervals further 

 east. Several examples of it may be found near the Cefn cave, 

 clinging to the rocky slope. This bed could not have been accumu- 

 lated before the glacial submergence, as it contains a few erratic 

 pebbles f , which must have been transported by ice from regions far 

 beyond the basin of the river Elwy. 



Before endeavouring to offer a general explanation of the mode 

 in which the various deposits were introduced into the Cefn and 

 Pont-newydd caves, it may be necessary to state that the drift- 

 deposits of the north-west of England and the borders of North 

 Wales are separable into : — (1) a lower stony Boulder-clay (with 

 glaciated stones), which to tho south of the Mersey and in the 

 eastern part of Wales can only be detected at intervals ; (2) a mid- 

 dle sand and gravel (without any large boulders or glaciated stones, 

 excepting a few among or near to the mountains), which extends 

 almost continuously over very wide areas, and often attains a thick- 

 ness of nearly 200 feet ; (3) an upper Boulder- or brick-clay (with 



* It likewise contains Eskdale granite. 



t Professor Hughes mentions the occurrence of felstone in this bed in Pont- 

 newydd cave. I saw a large boulder of very typical Arenig felstone, about half- 

 way between Denbigh and Cefn ; and I believe that a boulder which may be seen 

 a short distance N.W. of the Cefn cave must have come from the same moun- 

 tain. 



