500 Notices of Memoirs— Dr. S. Hicks — Rochs of N. Devon. 



11. — A Comparison between the Rocks of South Pembrokeshire 

 AND those of North Devon. By Henry Hicks, M.D., F.R.S., 

 Sec. Geol. Soc. 



THE clear succession from the Silurian rocks to the Carboniferous 

 to be observed in many sections in South Pembrokeshire offers, 

 in the author's opinion, the key to the true interpretation of the 

 succession in the rocks of North Devon, for there cannot be a doubt 

 that the post-Carboniferous earth-movements which so powerfully 

 affected and folded the beds in North Devon extended into and pro- 

 duced almost identical results in South Pembrokeshire. In the latter 

 area, however, the succession remains clearer, and can be traced more 

 continuously. 



The base of the Silurian (Upper Silurian Survey) is exposed at 

 many points, and the lower beds repose transgressively on the 

 Ordovician, and even on some pre-Cambrian rocks. Near Johnston 

 and Stoney Slade the conglomerate contains numerous pebbles of 

 the Johnston and Great Hill granite as well as of other igneous 

 masses which were formerly supposed to have been intrusive in 

 these beds. From the Silurian to the Carboniferous beds there does 

 not appear to be any marked break in the series ; moreover, all these 

 beds were folded together and suffered equally by the movements 

 which affected the area. The axes of the folds strike from about 

 W.N.W. to E.S.E, The movements, therefore, at this time were in 

 a nearly opposite direction to those which affected the Ordovician 

 and Cambrian rocks at the close of the Ordovician period. Within 

 the broken anticlinal folds portions of the old land surfaces have 

 been exposed in several places by denudation. 



The succession exposed in this area and the effects produced by the 

 earth-movements so nearly resemble those already described by the 

 author as occurring in North Devon, that he is convinced that the 

 beds must have been deposited contemporaneously in one continuous 

 subsiding area, and that the differences recognizable are chiefly in 

 the basal beds, which were deposited on an uneven land surface. 



ni. — On the Evidences of Glacial Action in Pembrokeshire, 

 AND the Direction of Ice-flow. By Henry Hicks, M,D., 

 E.R.S., Sec. Geol. Soc. 



THE occurrence of ice-scratched rocks and of northern erratics in 

 North-west Pembrokeshire has already been mentioned by the 

 author, but in this paper he brings forward additional evidence to 

 show that, during the Glacial period, a great thickness of land-ice 

 must have passed over Pembrokeshire. 



The glacial strise, which are so well preserved under the drift 

 along the north-west coast, especially at Whitesand Bay, show that 

 the ice travelled over that area mainly from a north-western direction. 

 The presence of erratics from North Wales and from Ireland would 

 tend to the conclusion that glaciers from these areas coalesced in 

 St. George's Channel, and that the ice which overspread Pembroke- 

 shire was derived from both these sources, as well, probably, as 

 from a flow extending down the channel from more northern areas. 



