D. MACKINTOSH ON HIGH-LEVEL MARINE DRIFTS. 



357 



erratic stones from a distance by floating ice, provided we admit that 

 Moel Tryf an may have returned the compliment ; and a number of 

 shell fragments which I found along with small flint chips certainly 

 looked as if both had been brought and deposited at the same time, 

 though their final juxtaposition in the lamina to which (in that part 

 of the section) they were limited must evidently have been the 

 result of rearrangement on the spot. 



12. High-level Gravel and Sand in other parts of Caernarvon- 

 shire. — Wear the summit-level of the pass of Llanberis, some years 

 ago, I saw a striking section of obliquely laminated sand and fine 

 gravel, probably about 1000 feet above the sea-level. The extent to 

 which the stones were rounded, the arrangement of the laminae, and 

 the position of the deposit (being away from any channel which 

 could have conducted a freshwater stream), all pointed to its being 

 of marine origin, though I did not see any shells. Above Bethesda, 

 near a farm-house marked Gwaun-y-gwiail on the Ordnance map 

 (probably about 1000 feet above the sea), a gravel-pit shows lami- 

 nated and contorted gravel and sand, in which (for reasons which 

 need not be stated) I had not time to look for shells ; but Trimmer 

 told Ramsay that he had found shells in that neighbourhood up to 

 from 1000 to 1200 feet above the sea. It does not seem to be 

 well known that Eamsay found shells in Boulder-clay on Pridd 

 Bryn-mawr (west of Llanberis) at a height of about 1000 feet above 

 the sea. 



13. High-level Gravel and Sand in Ireland. — It may be neces- 

 sary to complete this account of high-level marine drifts in the 

 western part of Wales b}^ adding a brief statement of what Close 

 found on the Three-rock Mountain near Dublin (see Geol. Mag. vol. i. 

 Decade ii. 1874). He collected shells from gravel-pits at 850 feet, 

 1000, 1100, and a little higher than 1200 feet above the sea. 

 The Three-Rock Mountain consists of granite ; but the stones com- 

 posing the gravel were very nearly all limestone, which must have 

 been brought by floating ice from the N.W. They were nearly all 

 subangular ; but the deposits partly consisted of clean stratified 

 gravel and sand [showing the action of the sea on the spot?]. He 

 believed that the shells were brought along with the stones by 

 floating ice, because both were scratched. He found more or less 

 clay above the shelly deposits, and was led to believe that the 

 mountain must have been submerged up to 1760 feet. The Three- 

 rook Mountain is related to Moel Tryfan by the altitude of its shelly 

 drifts, and by the direction of the floating ice which brought its 

 erratic stones. 



III. Deposits on Halkin Mountain, Flintshire. 



Several years ago I read an account of these deposits before the 

 Chester Natural-Science Society. Since then they have been mapped 

 by the Geological Surveyors. The mountain, including its westerly 

 continuation as far as the Yale of Clwyd, is a plateau surrounded on 

 all sides by lower ground, so as to render it certain that the mounds 



Q. J. G. S. No. 147. 2 b 



