382 ME. A. STRAHAN ON THE GLACIATION OF 



north-east across Morecambe and Liverpool Bays*. Dr. Ricketts, 

 on the other hand, opposes the idea of " a monstrous glacier filling 

 the Irish Sea, or of one extending from the mountains of Cum- 

 berland across the Bay of Liverpool," and attributes the scratches 

 to glaciers descending the valleys. Mr. Mackintosh, in his nume- 

 rous papers communicated to this Society, remarks on the fact 

 that the striae run in the main directions in which erratics have 

 travelled from their respective points of dispersion, and attributes 

 the dispersal of the erratics to floating ice. The production of 

 the striae also he assigns to the same agent, and remarks, " all 

 the striated and planed rock-surfaces around Birkenhead and Liver- 

 pool are covered, so far as I have seen, by Upper Boulder-clay 

 which, without any change in its character or intervening de- 

 tritus, touches the striated rock-surfaces." He concludes that the 

 overlying clay was deposited while the striated surface was still 

 submerged f. 



Tn 1883 Mr. Mellard Eeade remarks that he has found no Shap 

 gTanite on the west side of the Pennine chain, and that the erratic 

 blocks are confined to the drainage-area of the Irish Sea. " This 

 fact," he adds, " seems to me fatal to the idea of an ice-sheet over- 

 riding the great watersheds, and points to a system of glaciers 

 radiating from mountain-nuclei. The distribution of the erratics, 

 as described, seems unaccountable on any theory excepting that of 

 their being sea-borne " %. 



Prof. T. M'^K. Hughes notes the easterly direction of the striae 

 around the Vale of Clwyd, and points out that the ice ignored the 

 vale. " Everything fits in with the hypothesis that the mixed Clwy- 

 dian drift belongs to a period when the glacier ice had receded, and 

 the sea was working away, sorting, and transporting the ancient 

 glacial drift " §. 



It is clear that neither in South Lancashire nor on the Welsh border 

 can the phenomena have been produced by any system of local 

 glaciation. A glacier formed in the valley of the Mersey would have 

 taken exactly the opposite direction to that in which it is probable 

 that the striating agent actually travelled: similarly a glacier formed 

 in the Yale of Clwyd would certainly travel along the vale to the 

 sea, down the uninterrupted slope of the Triassic rocks, rather than 

 go out of its way to traverse the lofty Silurian hills on the west. 

 Nor is there any trace of moraines in any of the valleys in the dis- 

 trict under description. The question thus resolves itself into the 

 consideration of two hypotheses, — first, that of two ice-sheets, an- 

 terior to the submergence, moving under the influence of gravitation 

 from north-north-west in Lancashire, and from west-south-west in 

 North Wales, and meeting at the border; secondly, that of field- 



* "How Anglesey became an Island," Quart. Journ. Geol. Soe. vol. xxxii. 

 (1876). 



t Quart. Journ. Geol. Soc. yoI. xxxv. p. 440 (1879). 



X "The Drift-beds of the North-west of England and North Wales. — 

 Part II.," Quart. Journ. Geol. Soc. vol. xxxix. p. 83 (1883). 



§ Proc. Chester Soc. Nat. Sci. part 3 (1885). 



