454 Kiigh Miller — Formation oj Rock-Basins. 



Eeference to the map of Sutheiiandsliire will show that in and near 

 the district of Assynt, the larger lochs trend parallel with Loch Assynt 

 itself, this parallelism being very marked, and the tendency to range 

 in a transverse line — in other words to lie alongside one another — 

 scarcely less so. Mr. Bonney has explained this arrangement on the 

 subsidence theory, by supposing the line of depression to extend 

 across parallel valleys, throwing them into boat-shaped hollows at 

 opposite points.^ Thus Lochs Fewn and Veyatie, L. Assynt, L. 

 Glen Coul, and L. More, would fit into a depression which Loch 

 Eriboll on the north, and the embayed side of Loch Broom on the 

 south, might be supposed to terminate and confirm. 



Between L. Assjmt and the Fewn-Veyatie line comes the moun- 

 tain Suilven, stretching its cathedral-like form in the same direction 

 and across the imaginary depression. Canisp and Queenaig have 

 similar relations to these or other lochs. 



Now the stratigraphical evidence furnished by these mountains 

 is such as is at once fatal to the theory, — plausible and seductive 

 though it undoubtedly might seem. The nearly horizontal lines of 

 stratification that traverse the naked sides of these mountains — lines 

 that a straight edge would nearly coincide with — furnish a positive 

 standard by which to test at least this theory, and comparing with 

 them the probable contours of the neighbouring lochs, the curved 

 lines of the latter are manifestly entirely at variance.' 



It will scarcely be to digress to follow this theory a little further. 

 There is another way in which the profile of neighbouring lines 

 might be affected by the depression of valleys into lake troughs. 

 Geologists of standing have traced ancient plains of marine denu- 

 dation by the lines connecting mountain and hill summits. Surely 

 recent depressions, when amounting to thousands of feet, might 

 visibly affect the general outlines of hill ranges bordering lakes 

 thus originated. Mr. Bonney finds an example of lakes arranged 

 athwart valleys in Como and its neighbours. Do the elevated walls 

 of the valleys in which Como, 2000 feet deep, and Maggiore, 2600 

 feet deep, are lodged, show a corresponding curve in their profile ? 

 The positive evidence of the soundings and of Mr. Bonney's observa- 

 tions tend, so far as I can judge, to support the subsidence theory in 

 the case of the former ; but the evidence cannot be complete until 

 it is proved either that no such depression can be expected, or that 

 it exists ; and Mr. Bonney's theory especially requires this. 



Passing now to the generalized argument I attempted to illustrate 

 by the Cambrians of Assynt, I may repeat that, considering the 

 multitudes of lakes and large tarns in the vicinity of the mountains 

 displaying in section the features on which I have insisted, it maj^ 

 well be thought unfavourable to a theory ascribing these to flexure, 



^ Quart. Journ. Geol. Soc, vol. xxix. p. 394, and vol. xxx. p. 488. 



^ I may refer to my father's description of these mountains as "barred by the 

 lines of nearly horizontal strata." On the Eed Sandstone, etc., Deposits of Assj-nt; 

 quoted in Murchison's Siluria, 3rd edit. p. 198. A fault crosses Suilven " East and 

 West" (Murchison, Quart. Journ. Geol. Soc, 1858), but has no direct relation to 

 the supposed line of depression. It is not contended that subsidence special to each 

 of the lochs is here absolutely disproved. 



