﻿I860.] 



NICOL N.W. HIGHLANDS. 



109 



beds rest conformably on each other, no amount of denudation can 

 ever alter their order, or cut out one or two members of the series ; 

 but along a line of fault the case is just the reverse : always, as 

 denudation proceeds, older and older beds will be brought to the 

 surface, and thus into contact with the gneiss. This will be readily 

 understood from the diagram fig. 1. As drawn, the limestone d is 

 shown in contact with the eastern gneiss a. A small amount of 

 denudation would bring first the fucoid-beds c 2 , then the quartzite 

 c x , the red sandstone b, and even the western gneiss, into contact 

 with the eastern gneiss. On the other hand, in the contrasted 

 section (fig. 2, p. 217) in vol. xvi. of the Journal of the Society, it 

 is evident that no amount of denudation could ever bring the 

 gneissic flagstones d 2 on the east into contact with the lower lime- 

 stones c 2 or quartzite c 1 , and still less with the Cambrian sandstone b. 

 But my sections show (and the fact cannot be disputed) that in 

 some places the limestone, in others (and more often) the quartzite, 

 in others the red sandstone, thus come into contact with the gneiss. 

 As a marked instance, I may refer to Loch Maree, where, in less 

 than a couple of miles, all these relations may be seen, as denudation 

 has been more or less extensive. In the hill on one side of the valley 

 it is limestone, in the low ground in the centre the red sandstone, and 

 then, on the other side, the quartzite. How " conformable upward 

 succession " can explain such relations I cannot comprehend. 



Third. That there is here a line of fault, and not of conformable 

 overlap, is proved by the nature of the formations. Though along 

 the line of fault, and especially where the disturbance has been 

 most violent, the quartzite is often much hardened and semifused, 

 still it is a decidedly fragmentary, granular rock. The gneiss or 

 mica-slates, said to rest on it, are no less distinctly crystalline in 

 structure. This is true even of the finest-grained of these strata. 

 Now, before we can accept the theory of superposition, this fact must 

 be explained. That a truly crystalline metamorphic rock should 

 rest on deposits, thousands of feet thick, of unaltered sandstones 

 and limestones with fossils, is so improbable, so contrary to all the 

 established principles of geology, that nothing but the most un- 

 doubted evidence and the failure of all other methods of explanation 

 would justify us in admitting the fact. In the Alps, where such 

 superposition of crystalline on unaltered strata is seen, the most 

 distinguished and experienced geologists have found it " necessary to 

 admit that the strata had been inverted, not by frequent folds .... 

 but in one enormous overthrow, so that over the wide horizontal 

 area, the uppermost strata, which might have been lying in troughs 

 or depressions due to some grand early plication, were covered by the 

 lateral extrusion over them of older and more crystalline masses*." 



* SirR. I. Murchison, " On the Structure of the Alps, &c.," Quart. G-eol. Journ. 

 vol. v. p. 248. I need hardly say that no locality is known to me in Scotland 

 where the crystalline strata overlie the limestone or quartzite in the clear manner 

 shown in the section (fig. 28, p. 246) to which the above extract refers. The 

 phenomena in some parts of Sutherland are more closely represented by fig. 4, 

 p. 182, fig. 16, p. 203, and fig. 19, p. 209, of the same valuable and instructive 

 memoir. 



