1867.] LUBBOCK PAKALLEL BOADS OF GLEN ROY. 93 



much alike. Now, if their breadth depended on the supply of matter 

 from above, it would depend on the time during which each was being 

 formed; or if the supply were not constant, then the variations in the 

 time and in the rate of supply must have just counterbalanced one 

 another ; and either of these hypotheses is, it must be admitted, very 

 improbable. If, however, they have been formed as I have ventured 

 to suggest, then this uniformity will also be accounted for, because 

 the water would tend to give them a certain slope, reaching to the 

 depth affected by waves ; and when these conditions were fulfilled 

 the hill-side would be in a state of equilibrium, and would remain 

 with little further alteration until, on a sinking of the water, the 

 formation of another shelf commenced. In fact the lower level of 

 the roads marks the lower edge of the disturbed water, just as their 

 upper edge coincides with its upper edge. We thus see why the 

 three shelves are so similar in size, and also why their width is least 

 when their inclination is greatest. 



We can also now clearly see why the lines " entirely disappear 

 when crossing any part which is greatly inclined;" and we obtain 

 an additional argument in favour of the " lake- " as against the 

 " sea- " theory. The action of the waves is, of course, most consi- 

 derable at the surface ; and the disturbance gradually diminishes 

 downwards, until we at length reach the undisturbed water. So 

 also the upper edge of the roads is weU marked, but the lower side 

 passes almost insensibly into the general slope of the hill. On Sir 

 C. LyeU's theory it seems to me that the reverse ought to have been 

 the case. 



Mr. Jamieson, fuU of his idea that the lines were " continuous 

 deltas," was naturally " struck with the remarkable absence of 

 deltas along the two upper lines." *' I do not think," he adds, " the 

 shorter course of the rivulets sufficient to account for this." Cer- 

 tainly not; the true explanation is, that the matter brought by 

 rivulets during the period of the upper shelves naturally went to 

 the bottom of the vaUey, and forms the base of the existing deltas. 

 If the valley were to be again filled up to the level of the highest 

 shelf, the deltas would not be formed at that level, but the matter 

 brought down by the streams would continue to be deposited almost 

 as at present. Only after it had built itself up to the height of the 

 higher shelf would the delta be formed at that level. 



It seems to me, therefore, that Mr. Chambers was more near the 

 truth than Dr. Macculloch, and that, if we realize to ourselves that 

 the action of the waves tended not to cast up, but to throw down 

 the materials which it moved, we simply and easily explain all the 

 various phenomena presented by these remarkable roads. It is 

 hardly necessary to add that the same explanation is of very wide 

 application. 



