836 J. GEIKIE ON THE GLACIAL PHENOMENA 



both shores of Traigh an Taobh-tuath. Between Borgh and Maodal 

 the till lies close in at the foot of the cliffs and precipices, and spreads 

 out seawards in low sloping ground. Similar appearances recur on 

 the opposite side of the bay ; the whole of this area, in short, seems, 

 during the glaciation of Harris, to have formed a sheltered recess, in 

 which the till was allowed to accumulate to a greater extent than 

 elsewhere. No such continuous deposits of till occur in North 

 Harris ; but patches are common enough, and these are almost in- 

 variably met with either in valleys that coincide in direction with 

 the primary glaciation, or sheltering on the Lee-seite of roches mou- 

 tonnees whose smooth faces look towards the south-east. The fact 

 that the till is so frequently found lying in considerable thickness in 

 the rear of prominent rocks, the Stoss-seite of which faces the direc- 

 tion whence the ice flowed, is sufficiently suggestive, and may be 

 observed in every part of the island. 



An examination of the till in such sheltered positions points even 

 more strongly to an ice-flow from the south-east. Thus at Clife 

 Sheileboist (Fig. 7) the till that shelters on the north-west side of 

 the hill shows a kind of rude arrangement of its stones and boulders, 

 which are inclined outwards and downwards from the rock against 

 which the deposit abuts. Similar appearances show themselves in 



Fig. 7. — Section of Till near Clife Sheileboist, South Harris. 



N.W. S.E. 



Eoad. 



a. Till, showing rudely bedded arrangement of stones in lee of rock. 



many other places along this part of the sea-coast; and they may also 

 be studied to great advantage in the numerous openings on the side of 

 the road leading from the Tarbert to Fincastle (Fig. 8). The pheno- 

 menon is well known on the mainland of Scotland, and has been de- 

 scribed by me elsewhere*. It shows how the till was gradually 

 piled up on the lee-side of rocks and hills, much in the same way 

 as detritus gathers behind a boulder in the bed of a stream. 



Although the rocks of Harris consist for the most part of gneiss, 

 and it is usually quite impossible to say how far any isolated boul- 

 der may have travelled, yet we may often detect in one and the same 

 section of till and gneiss certain boulders and the parent rock from 

 which these have been derived. In every case of this kind that 

 came under our observation the stones invariably lay to the west or 

 north-west of their parent rock. The truncated ends of the gneiss 

 were bruised and bent over towards the north-west, and the frag- 



Great Ice Age,' 2nd edit. p. 18. 



