1889.] on the Highlands of Scotland and the West of Ireland. 541 



It is difficult to suppose that such colossal displacements and frac- 

 tures of the crust should not have powerfully affected the superficial 

 topography of the time. They may have produced a high mountain 

 range, or a succession of parallel ranges, extending along the north- 

 west of Europe. The existence of some such mass of land is needed 

 to account for the vast piles of sediment of which the Paleeozoic, 

 Secondary, and Tertiary formations have been built up. So great, 

 however, is the antiquity of these terrestrial movements, so continual 

 and gigantic has been the denudation, and so repeated have been the 

 oscillations of level, that the upheaved land has been reduced to the 

 fragments that now form the Highlands and Islands of the west of 

 Ireland, of Scotland, and of Scandinavia. 



It is quite clear that during the disturbances in the north-west 

 region the main thrust came from the eastward. It will be interesting 

 to discover how far towards the east these disturbances affected the 

 structure of the rocks beneath. That it reached across the whole 

 breadth of the Scottish Highlands, that is for a distance of 100 to 

 130 miles, can be conclusively proved. That it extended much 

 further and embraced within its area the whole of the Silurian regions 

 of the three kingdoms can, I think, be shown to be highly probable. 



To understand this part of the problem it is necessary to consider 

 the structure of the ground immediately to the east of the belt of 

 extreme complication in the north-west Highlands. I have said that 

 the displacements and metamorphism "increased in intensity from 

 west to east, until at last, by a final gigantic thrust, a series of re- 

 constructed schists has been driven over rocks whose origin can still 

 be determined. Among these eastern schists it is occasionally possible 

 to detect more or less reliable traces of the original rocks out of the 

 crushing down of which they have been formed. Thus we find in 

 the northern part of the area slices of Archaean and eruptive rocks, 

 and in the south an increasing amount of material which has been 

 derived from the destruction of the red Cambrian sandstones. It is 

 tolerably evident that in the broad band of country which extends 

 from the belt of complication eastwards to the Moray Firth and the 

 line of the Great Glen, and embraces the mountainous tracts of 

 Sutherland, Ross, western Inverness-shire, and north-western Argyll- 

 shire, the lower parts of the Geological Eecord are repeated again 

 and again. It is mainly the Archaean platform, with its covering of 

 Cambrian sandstones, and possibly the lower parts of the Silurian 

 series, which have been broken up, plicated, crushed, and converted 

 into the series of crystalline schists that form the picturesque heights 

 of Ben Hope and Ben Klibric southward to Moidart and Morven. 

 Nevertheless when this wild tract of country comes to be mapped out 

 in detail, there will probably be found intercalated bands of higher 

 formations which have here and there been caught in folds of tho 

 lower rocks. 



But when we pass eastwards from the Great Glen into the moun- 

 tains of eastern Inverness-shire, Perthshire, and the south-western 



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