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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Dee. 5, 



A comparatively very small amount of inversion and extrusion of 

 older crystalline masses will suffice to explain any of tlie Scottish 

 sections, even as drawn and described by the advocates of an over- 

 lying " younger gneiss." That such inversion and extrusion of 

 older masses on younger (though not of gneiss on quartzite) do 

 occur in this region of Scotland, and close to this line of fault, is 

 shown in the section of Sailmhore (fig. 13, p. 104) ; and, until some 

 rational theory is produced of the mode in which an overlying 

 formation, hundreds of square miles in extent and thousands of feet 

 in thickness, can have been metamorphosed, whilst the underlying 

 formation, of equal thickness and scarcely less in extent, has escaped, 

 we shall be justified in admitting inversions and extrusion equal to 

 those in the Alps. 



Strike of the beds. — Two general facts have been adduced in proof 

 of the diversity of age of the gneiss on the west coast of Sutherland 

 and that forming the interior of the country — the diversity in strike 

 and in mineral character. Now it is evident that the relative age of 

 the gneiss in these two regions is an entirely different question from 

 the question whether or not the eastern gneiss overlies the quartzite. 

 I have more than once stated that the gneiss of Scotland probably be- 

 longs in part to distinct geological periods, and have specially pointed 

 out " the great tract of gneiss with associated quartzite and limestone, 

 stretching from Aberdeenshire through Perthshire to the Breadal- 

 bane Highlands of Argyleshire, as a newer formation*." And such 

 newer beds might also occur in Sutherland and yet not overlie the 

 quartzite. In regard to the strike of the gneiss, I mentioned in my 

 former paper that in the western region " its general direction was 

 to the N.W.," whereas, as Macculloch had long before stated, in the 

 centre of the country it was more commonly " to the south-east- 

 ward f." But this distinction is not universal. The mica- slate of 

 Far-out Head clips to the S.E. ; and, as Mr. Cunningham shows, 

 the gneiss round Canisp and Suilven has also a N".E. strike, and a 

 similar strike with S.E. dip is common in the south of the Lewis. 

 On the other hand, a N.W. strike prevails in Strath Oykill and the 

 lower part of Loch Shin, and in Ross-shire similar diversity occurs. 

 This sudden and entire change in the strike of the rocks in different 

 parts of the Highlands is, however, a very marked feature, and is 

 clearly connected with that peculiarity of structure exhibited by the 

 previous sections. The country does not consist of one large mass 

 of strata, but of fragments, irregular in form and of more or less 

 extent, and each subject to its own laws of position. They may be 

 well compared to the shoals of ice seen on a river-bank in spring, 

 each turned in its own direction, with little reference to the frag- 

 ments beside it. 



There can be no doubt, however, that the country has undergone 

 a very general disturbance subsequent to the deposition of the 



* Note explanatory of the Geol. Map of Scotland, pp. 2, 3 ; and the Section 

 engraved on the Map. See also " On the Slate Rocks of Easdale, &c.," Quart. 

 Journ. Geol. Soc. vol. xv. p. 110. 



t Quart. Journ. Geol. Soc. vol. xiii. pp. 35, 37. 



