Dr. Mac Culloch on the Parallel Roads of Glen Roy. 381 



ally affecting the notions which have, with otherwise much appear- 

 ance of reason, been entertained relating to the ancient state and 

 posterior changes of the great Caledonian valley. It is conceived by 

 many persons that Scotland was once entirely or partially divided 

 in this place by the sea, the highest elevation of the present land 

 being, as we have already seen, ninety feet. By the constant descent 

 and accumulation of alluvium from the mountains, it is supposed that 

 the dams have been formed which now separate Loch Oich both 

 from Loch Ness and Loch Lochy, while these lakes have been dis- 

 joined from the sea by the large alluvial plains that now extend from 

 them at each end along the courses of the Lochy and the Ness. 

 The operations required in constructing the Caledonian canal have 

 ascertained the reality and extent of these alluvia, while daily obser- 

 vation shows that they are, in many places at least, receiving an 

 augmentation which has a tendency at some far distant period to 

 obliterate the lakes, and convert the whole into one prolonged strath, 

 of which the future summit will be Loch Oich, or some point in its 

 vicinity. If indeed we examine the changes which the lakes of 

 Scotland are now undergoing, we shall find that they are receiving 

 accumulations of alluvial matter at all the points where they are fed 

 by the surrounding streams, while a comparatively small quantity of 

 this alluvium is carried from their exits towards the sea. The 

 result of this operation is to obliterate them, and to convert them 

 into alluvial valleys or straths. Instances of this revolution more 

 or less perfected are numerous, while no case of the obliteration of 

 a lake by drainage, similar to that of Glen Roy, can be pointed out. 

 A different series of operations must have been required for this 

 effect, and we have to reconcile the opposite processes which at 

 different times have been carried on in the same place ; in the pre- 

 sent case for example, in the course of the Caledonian valley. It is 

 Vol. iv. 3 c 



