TEANSACTIONS OF SECTION C. 649 



l^lississlppi Valley, to 230 feet on the coast of Maine, and to 500 feet at Montreal 

 and in the valley of the Ottawa Eiver. 



The question of a succession of Glacial epochs has narrowed itself down in 

 America to the question whether or not there have heen two epochs, or one epoch, 

 with minor halts in the recession of the ice. So far as my own observation goes, 

 and it has been extensive, the complete separation between the epochs does not 

 seem to be proved. The forest beds are all pretty well towards the southern part 

 of the area, and are many of them probably pre- Glacial, while others are of such a 

 nature that they might have accumulated in a comparatively brief episode of oscilla- 

 tion of the ice front. The terminal moraine of what is called the Second Glacial 

 epoch, which stretches with a good degree of continuity from the Atlantic to the 

 Mississippi, may well enough be regarded as a moraine of retrocession, of which there 

 are numerous other instances, on a smaller scale, both north and south of this. 



5. Oil the Evidences of Glacial Action in Pemhrolceshire, and the Direction oj 

 Ice-flow. Bjj Henry Hicks, M.D., F.B.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 much additional evidence to show that, during the glacial period, a 

 great thickness of land-ice must have passed over Pembrokeshire. 



The glacial stripe 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 Pem- 

 brokeshire was derived from both of these sources, as well, probably, as from a flow 

 extending down the channel from more northern areas. Although there are in the 

 district many northern erratics, notably a large boulder of granite and another of 

 picrite, which the author found on Porthlisky farm, two miles south-west of St. 

 David's, yet by far the majority are of local origin and can be traced back to the parent 

 rocks. The gi-eat igneous masses which now form such conspicuous hills along the 

 north coast yielded most of the boulders, many of very large size, which are so 

 freely spread over the undulating land reaching to the coast of St. Bride's Bay. 

 There are clear evidences to show that this bay was itself overspread by a great 

 thickness of drift from these hills. The intervening pre-glacial valleys were also 

 filled by this drift, and the plains and rising grounds up to heights of between 

 300 and 400 feet still retain evidences of its former presence, and many perched 

 blocks. Excellent sections of unstratified drift, containing large ice-scratched 

 boulders, are exposed in Whitesand Bay, and a thickness of several feet of an 

 irregidarly stratified sand was, some time since, exposed under the boulder clay on 

 the east side of the bay. Chalk flints have been found at heights of over 300 feet, 

 probably having been "brought from Ireland. The picrite boulder already referred 

 to has been shown by Professor Bonney to resemble masses of that rock exposed in 

 Carnarvonshire and Anglesea, and the granite boidder, which before it was broken 

 must have been over 7 feet in length and 3 to 4 feet in thickness, is identical with 

 a porphyritic granite exposed in Anglesea, but not found anywhere in Pembroke- 

 Bhire. The evidences, therefore, which go to prove that Pembrokeshire was buried 

 under an ice-sheet that must have spread southwards into the Bristol Channel, 

 are, the presence of many northern erratics, both as perched blocks and in drifts at 

 heights above 300 feet, ice-scratched, smoothed and polished rock surfaces, and, in 

 places, much crushing and bending of some of the strata ; also great dispersions of 

 boulders from igneous rocks on the north coast in a south-west direction, and some 

 well-marked examples of ' crag and tail.' 



