546 T. Mcllanl Beade— 



area of shelly marine Boulder-clay, with sand and gravel beds 

 of great comhined thickness, extending from sea-level to 1,061 feet, 

 with a possible higher development of several hundred feet, and 

 in no sense can these high-level drifts be called "sporadic" de- 

 posits. They ai - e one and the same thing with the Low-level Boulder- 

 clay and Sands, with the stratification more highly developed. 



These Ayrshire high-level shells have, in the majority of cases, 

 been taken, not from sand and gravel beds, but from the Boulder- 

 clay, and in that respect they are most important and unique. In 

 the first discovered and classical example of Moel Tryfaen the 

 shells are found in sands and gravels at a maximum level of 1,400 

 feet 1 ; at Moel-y-Crio, 2 Flintshire, in sands and gravels at 982 feet; 

 on the range of hills from Minera to Llangollen, first discovered 

 by Mr. Daniel Mackintosh, from 1,000 to 1,200 feet; also in sands 

 and gravels at Gloppa, near Oswestry, at 1,100 to 1,200 feet, 

 described by Mr. Nicholson 3 ; in stratified beds of sand and gravel, 

 about 100 feet thick; at the "Setter Dog" before mentioned, 

 near Macclesfield, discovered by Prestwich, also in sands and 

 gravels, at a level of about 1,200 feet. In fact, before Mr. Smith's 

 discoveries in Ayrshire, the whole of the known shelly drifts were 

 classified as High-level Shelly Sands and Gravels. 4 Curiously 

 enough, in the sister island the High-level Shelly Drifts discovered 

 by the Bev. Maxwell Close were in gravelly sand, the prepon- 

 derating rock being Carboniferous Limestone. Here, however, 

 these drifts can be traced continuously up the valleys from sea-level 

 to their highest development on the Three Bock Mountain. 5 



There are also to be found in many localities shelly drifts at 

 intermediate levels, and sometimes well developed. Dr. Charles 

 Callaway has lately described those of Shropshire, in a paper read 

 before the British Association, Liverpool Meeting, 6 in which he 

 arrives at pretty much the same conclusions with regard to them 

 that I do myself. 



Before the Ayrshire deposits were discovered, it seemed some- 

 what of a mystei-y why the High-level Shelly Drifts should be 

 so commonly sands and gravels, for these materials are obviously 

 less calculated to preserve the marine calcareous exuviaa than clay. 

 In the case of the Dublin and Wicklow High-level Drifts, this 

 may be accounted for by the enormous quantity of limestone gravel 



1 These deposits have been often visited and described, but the most detailed 

 account of them -will be found in the Proceedings of the Liverpool Geological 

 Society, Session 1892-3. 



2 Memoirs of Geol. Survey — Mold, Flint, and Ruthin, p. 139. 



3 Q.J.G.S. 1892. 



4 Marine shells are recorded from Bacup, Lancashire, 800 feet above sea-level, 

 •which appear to have come from Boulder-clay. — H. Bolton, Trans. Manchester 

 Geol. Soc, vol. xxi, pp. 574-6. See also Boeder, ibid., 607-19. 



5 "Dublin and Wicklow Shelly Drift": Proc. Liverpool Geol. Soc, Session 

 1893-4. Mr. Joseph Wright, F.G S., records the occurrence of marine Bould r- 

 clay in Divis, co. Antrim, at between 1,300 and 1,400 feet.— Proc. Belfast Nat. 

 Field Club, 1894-5 (2), iv, pp. 215-6. 



6 "Notes on the Superficial Deposits of North Shropshire" : Geol. Magazine, 

 November, 1896, p. 482. 



