OP THE OUTER HEBRIDES. 8G5 



was of any size, as one may judge not only from the position of 

 their moraines, bnt from the size of the valleys and the capacity of 

 the feeding-grounds. 



In leaving the subject of glaciation, a word or two may^be added 

 on the very notable absence of kames. Wot a trace of these was 

 met with between the Butt and Barra Head. All this is quite in 

 keeping with the view that our kames owe their origin to torrential 

 waters flowing under and upon, and escaping at the margins of, the 

 melting mer de glace. Their remarkable distribution on the main- 

 land of Scotland shows that this was their origin ; they were 

 deposited and heaped up by water flowing from higher to lower 

 levels. Hence their contents become finer-grained and better water- 

 worn the further they are traced from their sources. In the lower 

 reaches of our broad valleys they are generally composed of well- 

 bedded sand and water-worn gravel ; in the upper parts of the 

 valleys they are not so well bedded, and their materials are generally 

 much coarser. Traced nearer to the mountains, they gradually pass 

 into irregular spreads and heaps of morainic gravels and debris. 

 Wow the broad flats of Lewis would not be traversed during the 

 melting of the ice-sheet by any great diluvial torrents ; for none of 

 the large valleys opens to the north. Nor is the configuration of 

 the ground in South Lewis and Harris a whit more favourable. 

 The valleys are short and steep, and not such as kames are ever 

 found in. We get the coarse morainic gravel and debris ; but those 

 materials have not travelled far enough to be sufficiently water- 

 worn, and the valleys are too narrow and steep to permit the 

 heaping up of banks of such incoherent materials. It is precisely 

 the same with the other islands of the Outer Hebrides. The con- 

 ditions for the formation of kames did not exist in the Long Island 

 any more than in the upper and central part of any mountain 

 district of the Northern Highlands. If kames were formed by 

 diluvial torrents derived from the melting of the Hebriclean ice, they 

 probably now lie submerged at a considerable distance from the 

 land, where they will occupy the same position ■ relatively to the 

 mountainous Hebrides as the kames of the Lowlands do to the 

 Highlands and Southern Uplands. Judging from all analogy, in- 

 deed, one can hardly doubt that the submarine plateau which 

 extends beyond the Outer Hebrides to the 100-fathoin line must be 

 more or less plentifully covered with drift sand and gravel, laid 

 down during the final retreat of the mer de glace. And I am thus 

 led to believe that much of the sand which is driven in such vast 

 quantities chiefly upon the western shores of the Outer Hebrides, 

 and which is gradually silting up the channels between the various 

 islands, is derived from drift -deposits corresponding in nature and 

 origin to the great diluvial sands of Northern Germany. 



4. Postglacial or recent submergence. — In concluding, I would 

 draw attention to the striking fact that there has been no consider- 

 able submergence of the Long Island since the close of the last 

 glacial period. No high-level beaches occur anywhere. No trace of 

 any undoubted postglacial occupation by the sea is found above a 

 Q. J. G. S. No. 136. 3 x 



