Dr. Mac Culloch on the Parallel Roads of Glen Roy. 38fi 



of the water. But if we examine any one of these furrows we 

 find that a portion of it, one half perhaps, and that of course the 

 most ancient as the most superficial, bears the unwasted mark of 

 the lines while the interior part, subject to a more modern destruc- 

 tion, exhibits no such impression. It follows therefore that the 

 lines are posterior in time to one portion of the period through 

 which the water has acted, and prior to the other. But if we now 

 conceive the water of the lake to have stood at the height of the 

 upper line, it is evident that the furrow itself could not have been 

 formed at that level and so far below it as to admit of a regular 

 deposit of a shore, such as I have supposed the lines to be, on its 

 sides ; as well as the repetition of two similar deposits occupying 

 precisely the same portion of the furrow, at one or two lower levels. 

 Since the descent of the torrent must have ceased at its contact 

 with the water, that part of the furrow which, from its now bearing 

 the mark of lines , is evidently of higher antiquity than the lake, 

 could not have been then formed ; nor on the two subsequent sink- 

 ings of the water can we conceive it to have been prolonged through 

 intervals of time so precisely equal, and with actions so precisely 

 similar, as to produce the appearances now visible. It is a more 

 probable supposition that the water which stood at the levels of 

 these three lines entered within the margin of the furrow so as to 

 deposit its shore on all that part which was then excavated ; while 

 the bottom which now shows no mark, has been formed by the 

 action of the same torrents since the final subsidence of the waters. 

 Water courses therefore have existed in times more ancient than 

 the lake, extending from the summits of the hills at least below the 

 present lowest line. But as these could not have existed but 

 in the absence of the lake, it follows that the lake itself was of a 

 posterior formation, and that the barriers which contained it were 



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