OF THE OUTER HEBRIDES. 



839 



the same nature are erratics of hornblende-rock, of mica-rock (a 

 rock composed almost exclusively of brown mica, with a very little 

 felspar), and of many other peculiar varieties, all of which, how- 

 ever, I have seen in place, interstratified with and passing into the 

 common basement-rock of these islands. Besides these, we occa- 

 sionally come upon boulders of basalt of much the same character as 

 the basalts of Skye ; but since dykes of this rock are common in 

 Harris and in the islands of the Outer Hebrides generally, it is not 

 necessary to suppose that these have been derived from other than 

 local sources. # m 



6. Morainic debris and Moraines.— Moramic debris and well- 

 marked hummocky moraines are of very common occurrence, espe- 

 cially in North Harris and the contiguous mountain-districts of 

 Lewis. In South Harris they are less conspicuous, and much _ of 

 what might be taken there for morainic debris is simply coarse till. 

 Morainic 5 mounds are scattered about the hill-sides in the neighbour- 

 hood of the Tarbert, and they are also commonly met with in all the 

 glens that descend from considerable elevations in North Harris. 

 Thus, in the valley occupied by Loch Lacasdail, well-marked moraines 

 run along both sides of the lake up to the height of 100 feet at least 

 above its surface. Small moraines are also conspicuous in the short 

 deep glens that open upon Loch Lacasdail. The glaciated hills that 

 face West Loch Tarbert from south and north have their lower 

 slopes thickly sprinkled with morainic mounds, the moraines being 

 crowded together upon the low ground through which the road from 

 the Tarbert to Stornoway passes. On the opposite side of the loch, 

 similar mounds are equally abundant. Some excellent examples of 

 moraines also occur at the mouth of Gleann Sgaodail and in all the 

 glens that come down from the Langa and the Cliseam. The Bealach 

 na Ciste likewise abounds in morainic debris and hummocky mo- 

 raines fine examples of which lie on the very watershed beyond the 

 upper lake. Indeed it may be said generally that moraines and 

 morainic debris are exceedingly plentiful in North Harris. _ 



In South Harris there are fewer mountain-glens, and moraines are 

 not so abundant. The finest examples we saw were at the mouth 

 of a valley near Traigh Losgcinntir, where the bed of the valley was 

 packed with well-formed hummocks and cones of moraine matter. 

 Nowhere else, as far as I know, do pronounced moraine mounds 

 occur in South Harris. Loose moraine-like debris is Sprinkled here 

 and there over the surface of the ground in the neighbourhood of 

 many of the hills ; but this material proved in many cases to be 

 merely decomposed or disintegrated till. 



With regard to the composition and structure of these moraines 

 little need^be said. They consist of earth, earthy sand, triturated 

 and comminuted grit, angular gravel and debris, and large an- 

 gular unpolished blocks of gneiss. Sometimes these blocks are sub- 

 ano-ular and rudely smoothed ; but this is quite exceptional. Occa- 

 sionally patches of gravel and sand make their appearance in the 

 moraines, and sometimes the morainic materials themselves show a 

 kind of rude bedding, the position of the stones indicating the direc- 



