184 Proceedings of the Royal Trish Academy. • 



devoid of a matrix, so that in many places where " foreigners " are not present, 

 it becomes ahiiost indistinguishable from weathered rock in situ. 



In the drifts of the lowland areas, lamination and stratification are seldom 

 seen, except in those cases where the impounding of late-glacial marginal 

 drainage with the formation of lakes has given rise to deltaic terraces. Any 

 departures in the drifts of the plains and valleys from a uniformly stiff and 

 tenacious deposit, in the form of lenticular bands of sand and gravel, are 

 quite local, and any arrangement of such is generally altered or reversed in 

 adjacent sections, when such are exposed. I have in consequence refrained 

 from inserting any drawings or sketches of such sections, as these would 

 serve no useful purpose. Moreover as the drift maintains the same general 

 character over large areas, I have deemed it unnecessary to give detailed 

 descriptions of sections, as these would involve constant repetition, incidentally 

 swelling this paper to unmanageable proportions.' Mention will be made of 

 those exposures only where the general characters are departed from. 



On account of the complexity of the outcrops of the metamorphic rocks, 

 and the large areas frequently covered by strata of a single type, it has been 

 found difficult to pick out definite rook trains of the members of this series ; 

 boulders may have travelled great distances, or may have been derived from 

 localities close at hand. Thus schists are usually useless for the purpose of 

 erratic tracking; their outcrops are too great, their variations too small. The 

 wide and irregular distribution of the diorites and epidiorites, the rapid 

 variations in texture to which they are prone, both in parent rock and drift 

 boulder, and the great and almost equally rapid variation in the amount of 

 foliation and metamorphism, which can be observed on specimens derived 

 from the same rock mass, militate against their successful employment as 

 indicators of the direction of ice-transport. The attempt was made in all the 

 earlier work, but had to be finally abandoned, as but little confidence was felt 

 in the results. Yet it may in general be said that to the lee of any diorite 

 outcrop — the direction of ice-motion having been ascertained from other 

 data — a very pronounced increase of the diorite erratics in the drifts is 

 noticeable. The erratics in these cases are clearly referable in bxilk to such a 

 diorite mass, and are confirmatory of the trend of the glaciation in the 

 immediate vicinity. 



When rocks occur of sufficiently distinctive type to be readily recognisable, 

 they are unfortunately frequently useless as indicators of ice-direction, for 



' It may here be mentioued that this papei-, when it was accepted three years ago 

 by the University of Leeds for the D.Sc. Degree, was almost twice its present size. The 

 reduction, necessary in these days of expensive publication, has involved the ruthless 

 sacrifice of much of the detailed observation upon which these conclusions are based. 



