GLACIAL ACTION. 41 



travelled blocks is the only one which we have seen ; no other 

 writer on Arran, that we know of, has turned his attention 

 to the subject. It is hoped, therefore, that the notices now 

 given will be the more acceptable. 



In Arran, as generally in other districts, the boulders be- 

 long to a particular period. The entire system of rocky 

 strata had been formed, and the existing inequalities of the 

 surface established; but in all probability the last upward 

 movement of the land, to which we have already often re- 

 ferred, had not taken place. The relative age, in fact, seems 

 to have coincided with that of the boulder-clay of Scotland, 

 or with the newer pleiocene era. Then, as regards the forces 

 concerned, we know only two natural agents capable of pro- 

 ducing the effects. These are currents of water and moving 

 masses of ice. Now, the former are totally inadequate to 

 carry forward masses of the enormous magnitude found here, 

 or even to transport the lesser blocks over all the obstacles 

 which they have surmounted, in their outward course from 

 the parent rock. Besides, they are often found " perched" 

 in situations where it is extremely improbable that currents 

 could have left them, and also crowded together in groups in 

 places quite open, and removed from the influence of eddies. 

 It is true, indeed, that the origiff of such currents can be 

 readily accounted for, by movements which we know to have 

 taken place the elevation, namely, of the mountain nucleus 

 from beneath the sea. We have only to suppose that it was 

 sudden and of considerable amount, and we have at once 

 generated a series of mighty pulses, which would carry the 

 disturbed waters, with their load of torn off materials, along 

 the surface of the lower lands still submerged. Rocky ma- 

 terials may thus have been swept away and re-arranged in 

 new situations, valleys scooped out, and extensive denuda- 

 tion effected. But the forces thus brought into play cannot 

 have been adequate to bear along the enormous masses, now 

 far separated from the parent rock ; and therefore we do not 

 hesitate, on this and the other grounds above stated, to con- 



