362 Dr. Mac Culloch on the Parallel Roads of Glen Roy. 



through Glen Spean at the same time as they flowed through Glen 

 Roy. This case is even more complicated than the one stated at the 

 beginning of the argument, it being impossible that a deluge of this 

 sudden nature and great magnitude could have taken place so as to 

 include Loch Laggan, without changes in the surface of the earth 

 at this place and beyond it, even greater than those which I first 

 pointed out, 



I shall not pursue the consequences of this hypothesis further. 

 Every person's imagination can supply additional difficulties, which 

 it would be tedious to follow to their ultimate ramifications. 



The next hypothesis which has been offered in explanation of the 

 lines of Glen Roy is, that they are the remains of water terraces 

 similar to those which are of common occurrence in the alluvial 

 straths of Scotland. 



Almost all the rivers, whether of greater or smaller dimensions, 

 that flow through these straths with small velocities, or over 

 planes of moderate inclination, are accompanied by lateral banks 

 lying at a distance from the actual bed of the stream. They 

 may in fact be considered as the deserted banks of the river itself, 

 which in forming a deeper course for its waters has at the same 

 time changed its ground laterally, leaving its ancient bed deserted 

 and bounded by one of the banks which formerly confined it, while 

 the other has been undermined and carried away by its opposite 

 lateral deviation. 



The ancient bank thus assumes the form of a terrace, with a slope 

 resembling that of a military work, and standing at that angle which 

 the peculiar circumstances of the soil enable it to maintain. Where 

 the action of the river has been such as to cut its way, constantly 

 deepening, through an alluvial plain, the surfaces of these terraces 



