838 J. GEIKIE ON THE GLACIAL PHENOMENA 



examined by me, that the occurrence of this solitary stranger, if it 

 really be one, is interesting. 



Many appearances which are familiar features in the till of the 

 Lowlands characterize the till where it occurs in greatest mass 

 along the west coast of South Harris. At Traigh Siar, for example, 

 we have an excellent section, showing the occurrence of bedding in 

 the till. The deposit at this place is a dark grey clay, very tough 

 and full of grit, with stones sparsely scattered through it. Enclosed 

 in this till are irregular lenticular beds of laminated clay and fine 

 sand, with lines of water-worn gravel, and sporadic angular and 

 subangular boulders. In places these bedded deposits become very 

 stony, shading off into, and becoming confusedly mixed up with, the 

 till. The stones in the till, I should mention, are usually subangu- 

 lar and blunted, and occasionally striated. Lines of stones may also 

 be traced in the till. All the beds evidently form part and parcel of 

 one and the same deposit, the rounded stones and gravel and bedded 

 portions pointing to the action of subglacial waters, and being gene- 

 rally of the same nature and origin as the similar intercalations in the 

 till of Switzerland. The whole rests upon a glaciated surface of 

 highly contorted gneiss. 



5. Erratics. — Next to the roches moutonnees of Harris, the most 

 conspicuous objects from a glacialist's point of view are the erratics 

 and perched blocks. These are common enough in most parts of 

 Harris, but they certainly occur in greatest abundance in North 

 Harris, some of the mountain- slopes being sprinkled with them 

 in myriads. They are of all sizes, from less than a foot across 

 to blocks measuring 20 feet and more in diameter. Most of the 

 larger ones and a large proportion of the smaller ones show no trace 

 of glacial abrasion, but are just such loose angular and weathered 

 blocks as are launched upon the sides of an Alpine glacier. Not un- 

 frequently, however, the boulders gave some evidence of glacial 

 grinding and smoothing, although, so far as I saw, none had pre- 

 served any strise. They are scattered promiscuously over the ground, 

 some dotting hill-tops, others crowding upon hill-slopes and valley- 

 bottoms. Sometimes they rest on till, at other times they are 

 perched on hummocky moraines and roches moutonnees. 



Nearly all are composed of gneiss or gneissic rocks, and have evi- 

 dently travelled no great distance. Indeed, in many cases, they are 

 quite local, the erratics at the lower end of a valley having come 

 from the hills drained by it. Amongst erratics which may be ex- 

 ceptions are certain large boulders of a blue calcareous greywacke or 

 impure limestone, which I saw on the lower slopes of the Cliseam, 

 overlooking the road to Stornoway. I have seen no rock like this 

 in place in any part of the Outer Hebrides ; yet it is quite possible 

 that the erratics may be derived from some unknown mass or bed of 

 limestone in the hilly region lying east of Loch Seaforth. Here and 

 there, both in North and South Harris, I met with large boulders of 

 a syenite strongly resembling some of the syenite of Skye ; but as the 

 gneiss of Harris now and again assumes a syenitic aspect, I have 

 but little doubt that the boulders referred to are of local origin. Of 



