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



argument even against that theory which I feel most inclined to 

 adopt. But I must now add, that the numerous difficulties which 

 attend it have suggested to others a different mode of explaining 

 the nature of the obstacles by which the water was maintained at 

 the requisite height. It has been supposed that the vallies have 

 been always the same as they are ai present found, and that the 

 imaginary dams were no other than the waters of the ocean ; or in 

 other words, that the sea itself formed the lake, to the action of 

 which on the sides of the hills the present levels must be attributed. 

 It will not require many words to examine the probability of this 

 supposition, since many of the arguments already used to refute 

 some of the hypotheses which have been examined, are equally 

 valid against this one. Unquestionably, numerous phenomena, too 

 well known to require notice here, justify us in believing that the 

 waters of the sea have in former times occupied higher levels than 

 they do at present ; although we are neither able to conjecture 

 whether these elevations were transitory or of long duration, nor to 

 form any rational conjecture of the causes by which they were 

 produced. In estimating the probability of this cause as applicable 

 to the solution of the phenomena in question, it must be recollected, 

 that the operation of the supposed lakes in producing the lines has 

 been tedious, if we may be allowed to judge from the apparently 

 slow operations of existing lakes in producing similar shores on 

 their margins. It must equally be remembered, that if Glen Roy 

 was then open to the sea, and that its lines are to be considered as 

 ancient sea shores, the ocean must have undergone three several 

 depressions of level at long and apparently equal intervals of time, 

 the last of which, it must be supposed, reduced it to its present 

 state. On considering the elevation of the uppermost line, it is 

 plain that the ocean must in this case have covered the greatest 



