630 MR. E. GREENLY ON THE GEOLOGY OF THE [Nov. 1 896, 



Local deflections through as much as 40° may be observed on 

 rock-faces no more than 3 feet high. 



There are large glacial furrows in a few places. 

 K-ock-bosses are generally moutonnes, on the N.ET.E. side. 



(b) Drifts. 



The drift is for the most part a typical, tough, brown Boulder 

 Clay, full of well- striated stones. 



It is very thick in the Yale of Llanfaes, probably not far from 

 100 feet, fine sections being seen on the coast between Penmon and 

 Beaumaris (Ramsay, op. cit. pp. 275-76). There is none on the 

 Carboniferous escarpment, but it thickens gradually on the dip- 

 slope, where there is one valley buried to a depth of 60 feet. The 

 brow formed by the schists is also free from drift, which, however, 

 again begins to fill hollows in the plateau to the westward. 



A great thickness of Boulder Clay comes in again near Llanddona 

 Church, where it forms cliffs about 50 feet high. Below Ffynnon-oer 

 this Boulder Clay suddenly rises to the 200-foot contour, forming an 

 inland cliff which must nearly follow a concealed rock-feature. 

 There has been much land-slipping here, probably upon buried 

 Ordovician shales. 



Such boulders as can be identified with local rocks have travelled 

 S.W.-S.S.W., a direction agreeing with that of the striae. Boulders 

 from the Welsh mountains have only been observed at Penmon ; but 

 rocks foreign to North Wales are abundant. 



The gravels associated with the drift along the Lleiniog shore have 

 been described by Ramsay, who notes their semi-consolidated state. 

 They contain faintly-striated stones. Similar gravels occur at 

 Llanddona. 



About Llanfaes there is a singular stoneless (or nearly stoneless) 

 red clay, as much as 10 feet thick. Its relations are not exposed. 



These phenomena seem to me to be best explained by the theory 

 of a confluence of bodies of glacier-ice coming from the north and 

 from the Caernarvonshire mountains respectively. Not only doe* 

 it explain the general south- westerly deflection of the striae and 

 boulders, but I think that the cross-hatching in the Penmon area can 

 also be understood by means of it. In that area complications must 

 have occurred. The influence of the great Ogwen glacier must have 

 been much less than it was farther west, and the glaciers of Aber 

 and Llanfairfechan only would have opposed the northern ice. On 

 comparing the extent and height of their catchment-basins I doubt 

 whether their combined force would amount to more than a quarter 

 of that of the Ogwen glacier. That they did offer opposition is 

 clear, for they extended at times as far as Penmon. But fluctua- 

 tion in the masses of the northern and southern streams would 

 enable the larger stream to pass on undeflected, especially if some 

 fluctuations did not affect both at once, which might well happen — 

 as their sources were so far apart. The local influence of some high 

 ground at Dinmor Point (west of which, moreover, there is an 



