T. Mellard Reade — Glacial Geology. 313 



are generally met with in the Drift of the plains. Drift with shells 

 is met with at various places at levels intermediate between the 

 Low-level Boulder-clay and sands and the High-level sands and 

 gravels. This Drift is usually laminated and current-bedded. At 

 Moel Tryfaen, where I devoted a good deal of study to the Drift, 

 there is a much greater preponderance of erratic stones, such as Lake 

 District rocks and Scotch granites, flints supposed to come from 

 Antrim, with an admixture of Carboniferous limestone which may 

 be from Anglesey, and true Anglesey crystalline schists, than is con- 

 tained in the Drift of the coastal plain which reaches from sea level 

 up to the 400 feet contour. It is rather a remarkable fact that 

 in this high-level Drift I found a piece of Shap Fells rock in the 

 form of a rounded pebble identified by Mr. Alfred Harker, F.G.S., 

 as from one of the numerous offshoots of the granite mass of Shap 

 Fells. I mention this specially because during the whole time I 

 have been observing I have never met with any Shap Fells granite 

 on this side of the Pennine Chain, either in Lancashire, Cheshire, or 

 North Wales. 



The High-level sands and gravels of Tryfaen are overlaid on the 

 eastern side of the excavations with a stony Till, evidently of local 

 derivation, and containing nearly all local rocks. In one place a 

 lamitiated bed of the sands inosculated with the Till, which also 

 contained pockets of the sand. This is a very striking feature which 

 has only been developed of late by the progress of the excavations. 

 The stones contained in the sands and gravels are much waterworn, 

 and there is a very much smaller proportion of them striated than 

 what we find in the Low-level Boulder-clay. The grains of sand are 

 also much rounded, waterworn, and polished. The Till also contains 

 a proportion of these highly polished grains, and I found on washing 

 some of the locally formed Till lying at a level of 800 feet above 

 the sea, between The Rivals and Mynydd Carnguwch, that this also 

 contained highly worn and polished quartz grains. 



Drift of the Coastal Plain adjoining Tryfaen. 



The Drift of the coastal plain adjoining Tryfaen is well exposed 

 in coast sections, and consists more largely of material from the 

 Snowdonian Range, both as regards boulders and the matrix, which 

 is largely made up of the debris of slate rock and small slate flakes. 

 An arched stratification is seen in some of the sections. The Till 

 can be examined in numerous sections cut by the streams through 

 the coastal plain, and a strict search almost everywhere yielded 

 pebbles of Eskdale and other erratic granites, but seldom any 

 fragments that could be described as " boulders." 



Mechanical analyses of twenty samples of the Till from various 

 localities, with one exception, yielded the rounded and polished 

 quartz grains. In some cases I found small shell fragments, and 

 ample evidence was accumulated that the drift of the coastal plain 

 was an intimate mixture of the debris of the Snowdonian rocks and 

 erratic material from the North, and in some cases from Anglesey. 



Tracing the coast sections south-westwardly, they gradually put 



