J. W. JT7DD ON THE SECONDARY ROCKS 0E SCOTLAND. 669 



Nor do I think that it will be possible to pause here. For, as has 

 been shown in the first part of this memoir, there are various depo- 

 sits of Mesozoic age in the counties of Sutherland, Ross, and Elgin, 

 the nearest of which lies 100 miles to the north-east of the 

 most northern patch of Secondary strata in the Western Isles ; and 

 these fragments of Secondary strata in the Eastern Highlands have, 

 as was there pointed out, escaped destruction by denudation only 

 in consequence of being let down many hundreds, or even thousands, 

 of feet below their original positions, and thus coming to be preserved 

 in the very heart of the much harder Palaeozoic masses. If, on the 

 other hand, we proceed from the patches of Secondary strata in the 

 Hebrides in a south-easterly direction, we find in Cumberland and 

 on the borders of Cheshire and Shropshire fragments of Liassic de- 

 posits faulted down into the midst of the older rocks ; and these 

 form a connecting link with wide-spreading tracts of the same strata 

 in the south-eastern part of England. 



In the face of these facts, I believe that it is impossible to avoid 

 the conclusion that the whole of the north and north-western por- 

 tions of the British archipelago — now sculptured by denudation into 

 a rugged mountain-land — were, like the south and south-eastern parts 

 of the same islands, to a great extent, if not completely, covered by 

 sedimentary deposits, ranging in age from the Carboniferous to the 

 Cretaceous inclusive ; and that, as a consequence, we must refer the 

 production of the striking and very characteristic features of those 

 Highland districts to the last great epoch of the earth's history — the 

 Tertiary — and very largely, indeed, to the latest portion of that 

 epoch, namely the Pliocene. 



It may be objected to this view concerning the recent date, geo- 

 logically speaking, of the origin of the existing surface-features of 

 the Scottish Highlands, that it is impossible to conceive of such a 

 vast amount of marine planing down and of subaerial gouging of a 

 series of rocks of the hardest character having been accomplished 

 within what we are sometimes tempted to regard as comparatively 

 short geological periods. But in reply to such an objection, I would 

 point to the enormous effects that have clearly been produced since 

 Miocene times in the Western Isles of Scotland, in the destruction 

 of the old volcanic cones of that area, and more especially in the 

 sculpturing of mountain-forms out of their intensely hard cores of 

 gabbro and hypersthenite ; to the work that has been accomplished 

 in the same area, probably since Pliocene times, as borne witness to 

 by the Scur of Eigg and the rocks of Beinn Shiant in Ardnamurchan ; 

 to the fact, which I have described in a former paper, that since the 

 period of the Upper Jurassic, thousands of feet of the Middle Old Eed 

 Sandstone or Caithness flagstones must have been removed from the 

 surface of Sutherland, as is clearly demonstrated by the preservation of 

 a portion of those beds by the singular double fault already described*. 

 But most strikingly of all is this fact of enormous denudation of the 

 Scottish Highlands during very recent geological periods demon- 

 strated by the occurrence of numerous post-Miocene faults, having 

 * Quart. Journ. Greol. Soc. vol. xxix. pp. 132-134. 



