238 ISLA. ALLUVIA. 



period, or at a later one, and from the gradual descent of 

 a luvial matter from the higher lands, is difficult to deter- 

 mine. The whole of this space is a flat peat moss, under 

 which is found a bed of sand and rolled stones with marine 

 shells ; rendering it probable, that, at some distant time, 

 Isla was here separated into two parts. The land is still 

 encroaching on Loch Gruinart ; the depth of high water 

 being only three feet, and permitting the sea to be 

 excluded by an embankment, with a considerable acqui- 

 sition of territory. 



Besides the alluvia now described, there are found in 

 Isla, in various places, rolled stones of considerable mag- 

 nitude and of various kinds. Among them are masses 

 of granite, a rock not existing in this chain, and of which 

 no transported fragments have occurred elsewhere among 

 the islands : the remainder are of substances which may 

 possibly be little removed from their natural situations, 

 since they are of trap, quartz rock, and schist. To inquire 

 whence these blocks of granite have been transported, 

 seems useless. Their dissimilarity of mineral character 

 prevents us from referring them to the distant mountains 

 of Arran, of which the relative situation offers sufficient 

 difficulties independent of this. If it be imagined that 

 they have been brought from Cruachan, the nearest mass 

 of granite, little is gained by the conjecture, since the 

 extent and intricacy of the present intervening tracts of 

 sea and land, offer an insuperable barrier to all rational 

 speculation on the changes to which the intermediate 

 space has been subjected. We must be content to repose 

 in the general conviction, that they are of foreign origin, 

 and have been transported to their present places when 

 the forms of the land were far different from what they 

 are now, and before these islands were separated from the 

 mainland. The existence of such masses however, serves 

 to confirm the supposition that the great alluvia already 

 described, and the obvious union of two islands into the 



