or Raised Beaches in Scotland, 8fC, 289 



several thousand feet, and are direct continuations of wide 

 plains near the coast, which are undoubtedly of marine origin.'* 



Mr Darwin refers to Sir T. Lauder Dick's paper in volume 

 9th of the Edinburgh Transactions, and to his own remarks 

 at page 58 of his Memoir on Glenroy, in further illustration of 

 the subject. I have looked into both. Sir Thomas describes, 

 at p. 37, four inclined shelves in Glenroy. They are far under 

 the horizontal shelves or parallel roads ; and, as he states, they 

 are not properly on the side of the hill, like the latter, but be- 

 tween the hill and the river, and the lowest is most inclined. 

 He notices similar shelves in Glean Spean, p. 41. 



The difference between the two deposits seems to be this. 

 In a narrow valley, a horizontal shelf like one of the parallel 

 roads is the product of the sea alone operating on the loose 

 matter brought down by rains, or eroded from the rocks by 

 the action of its own waves, during a period of rest when it stood 

 at one level. On the other hand, an inclined shelf is the product 

 of the sea, modified by the action of a large riter flowing through 

 the valley, and bearing detritus ; and it presents the sum of 

 the operations of the sea and the river at a succession of dif- 

 ferent levels, when the sea was subsiding. Each of the inclined 

 shelves in Glenroy is a remnant of a deposit which once ex- 

 tended across the valley in a curved line, and formed its bot- 

 tom. The parallel roads never extended across the valley, but 

 were originally, what they are still, mere fringes of loose matter 

 at the margin of the sea. 



It is, indeed, obvious, on a little reflection, that a continued 

 and equable subsidence of the sea would leave an alluvial depo- 

 sit in the bottom of the valley with a surface pretty regularly 

 inclined. It is only the case of an intermittent subsidence that 

 presents any difficulty, and of this difficulty Mr Darwin has 

 ofl'ered a solution which is at least plausible. The floods in 

 a river like the Tay would go far to obliterate irregularities of 

 outline as they arose, by sweeping off" prominent parts and 

 filling up cavities. 



