Chaklesworth — Glacial Geology of North- West of Ireland. 1 83 



glacial material on the laud is probably to be regarded as merely au 

 insignificant remnant of the total amount eroded and transported by the sea- 

 ward-moving glaciers. 



In the highlands of Donegal, the granite and quartzite outcrops which form 

 ridges are practically destitute of drift, while the relatively low-lying strips 

 of schist country serve as the principal receptacles of the glacial deposits. 



The boulder-clay seldom, if ever, assumes a level surface, for the ice in its 

 passage has induced the druiulin or subdued drumlin type of scenery. The 

 major axes of these drumlin mounds present, as usual; a general parallelism 

 with the direction of ice motion, and serve as unmistakable indicators of 

 direction, where striae are neither preserved nor exposed. These drumlins 

 are necessarily confined to the areas of thick drift, and are most typically 

 and abundantly encountered in the neighbourliood of Donegal Bay.' 



From the lai'ger spreads of drift, long tongues run up the smaller valleys. 

 It clings in gradually thinning sheets to the hillsides, and finally dies away, 

 leaving only detached patches in sheltered spots, such as small hollows 

 between bosses and ridges of solid rock, and the bottoms of little ravines and 

 stream gullies. Generally speaking, the drift has been removed from the 

 higher ridges and steeper faces, where the slopes were too abrupt for its 

 permanent lodgment. 



Opportunities for the examination of the drift are not abundant. Good 

 exposures are relatively few, and are practically confined to stream and river 

 banks and to coastal sections ; the slopes of railway cuttings are usually 

 soiled over and grass-grown, so that little or no information can be gleaned 

 from them ; while, under the extensive peat moors, the drift deposits are a 

 sealed book. In general, the drift, as elsewhere, partakes largely of the 

 character of the rocks upon which it immediately rests; on granite, it is 

 chiefly granitic, on quartzite, quartzitic, and on schists is largely composed of 

 these rocks. It seldom assumes the character of a true boulder clay, since 

 argillaceous material for the formation of a clayey matrix is not largely 

 available ; any such matrix present has to a very great extent been formed 

 by the breaking down of the softer schists, and is present in this form in 

 practically all the area examined, except where Carboniferous rocks play the 

 leading part in the build of the country. For this reason there is a sameness 

 in the matrix of the drift, both in texture and in colour, throughout much of 

 the highland region of Donegal, Inishowen, and the Sperrin Mountains. 



On the higher hill slopes, the drift is a stony accumulation, practically 



' Representations of some of tliese features around Donegal Bay are given by W. B. 

 Wright in Tlie Quarternary Ice Age, figs. 15-18. 



