480 CUMBKAY (GREAT). GEOLOGY* 



great waste which, in many of these cases, the land has 

 undergone from the action of the sea. Passing over that 

 which might be deduced from these appearances in the 

 sound of Isla, and which bespeak a once nearer approxi- 

 mation of the opposite shores, it is sufficient to contem- 

 plate the southern coast of Arran only. Here, a con- 

 siderable range of long outstanding dykes is now to be 

 seen, forming natural piers in the sea. It is scarcely to be 

 questioned that these were once surrounded, or their 

 intervals filled, by solid land ; but to what height, cannot 

 now be conjectured, as the veins themselves bear marks of 

 ruin and degradation. The same remarks are applicable 

 to many other parts of this island, as well as to Pabba 

 and other shores where similar prolonged dykes occur ; 

 but I need not point out more of these, satisfied with 

 having indicated the most perfect record which geology 

 affords of the wasting action of the sea upon the land. 



The other case, that of the outstanding inland dykes, 

 such as those of Cumbray, and the more conspicuous 

 examples in Isla and Mull, is more difficult of explanation. 

 It is equally evident however, even in these instances, 

 that the surrounding strata must once have existed at 

 least at the same level as the summits of the present 

 dykes ; nor can any obvious causes now be traced by 

 the operation of which so great a removal of land has 

 been effected. There are no rivers in any of the instances 

 enumerated, to which it could be attributed ; nor indeed 

 could any action of a river be imagined, capable of pro- 

 ducing those effects on surfaces so irregular. They have 

 probably resulted from the tedious operation of the at- 

 mosphere : the rains and the frost first loosening the 

 surface of the rocks, and the slow drainage of the surface 

 waters causing the subsequent descent of the pulverized 

 materials to the lower grounds; where they accumulate 

 to form the ordinary soil that covers the substratum. In 

 this way, probably, many of those accumulations which 

 huve often been attributed to diluvian causes, are formed ; 



