89 



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 belong 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 referred, 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 

 producing the effects. These are currents of water and moving 

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

 ward 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 to- 

 gether in groups in places quite open, and removed from the influence 

 of eddies. It is true, indeed, that the origin 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 con- 

 siderable 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 sub- 

 merged. Rocky materials may thus have been swept away, and 

 re-arranged in new situations, valleys scooped out, and extensive denu- 

 dations 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 conclude that moving masses of 

 ice were the transporting agents. In the passage of glacier ice adown 

 the valleys, and the buoyancy of floating bergs, forces of sufficient 

 energy would be lodged to carry the largest masses ; and this agency 

 we know, as already pointed out (Art. 11), is adequate to produce 

 the various phenomena of transport, grouping, and " perched blocks." 



60. We must conclude, then, that the northern mountains formed a 

 mass of ice-covered land, with glaciers in the valleys reaching the 

 bold shores of the sea of that period. From the extremities of these, 

 rock-bearing masses of ice, of which at least a few must have been 

 considerable bergs, floated away, and stranding or melting, threw 



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