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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Dec. 5, 



have been chosen, but are those brought forward as the proofs on 

 which the opposite theory is founded ; yet in not one of them have 

 we found that regular continuous upward succession which this 

 theory requires, but in every one of them irruptions of igneous in- 

 trusive rocks, and other indications of faults and disturbance, de- 

 priving them of all weight as evidence of regular order. Here, 

 therefore, I might have left the question, satisfied with this appeal 

 to special sections ; but there are a few more general facts, leading 

 to the same conclusion, which require a short notice. In order to 

 perceive the full force of these facts as bearing on the present ques- 

 tion, it must ever be kept in mind that this region has undergone a 

 most enormous amount of denudation — strata of at least 2000 to 

 3000 feet in thickness having in some places been swept away from 

 the surface ; consequently, if there be here a line of conformable 

 overlap, all the beds that dip east (the so-called " upper gneiss," 

 the limestone, and quartzite) must have originally extended much 

 further to the west. 



First. The mode of distribution of the rocks is altogether incon- 

 sistent with the hypothesis that the eastern gneiss overlies the red 

 sandstone or quartzite. The red sandstone, with a width from east 

 to west of thirty to fifty miles, is seen in innumerable places — at 

 Stornoway, Cape Wrath, Assynt, Gairloch, Skye, resting for miles 

 in all directions on the gneiss. So also the quartzite, with a breadth 

 of ten or twelve miles, is everywhere clearly seen to rest on the red 

 sandstone. Mile after mile, from north to south and east to west, 

 from mountain-top to mountain-top, from valley to valley, this rela- 

 tion may be traced. And thus also it is with the limestone, though 

 this formation is now of such Hmited dimensions. In every locality 

 where it occurs — Durness, Emboli, Loch More, Assynt, Ullapool, 

 Loch Maree, Loch Keeshorn, it is seen resting on the quartzite. 

 This relation can be traced round and round isolated masses of the 

 limestone, and across synclinal basins of miles in extent. But how 

 does it stand with the next step in the series, the so-called " upper 

 gneiss " or mica-slate ? This gneiss extends for fifty or a hundred 

 miles to the east, and, we are told, conformably overlies the quartz- 

 ite or the limestone, for a hundred miles from north to south ; and 

 for what distance to the east or west of the line of junction has this 

 overlap been observed ? Nowhere for more than a few feet, or yards, 

 at one or two widely separated intervals, has this overlap ever been 

 even alledged to occur. "We seek in vain for any isolated portion of 

 mica-slate resting on quartzite or limestone, on the west of this line 

 of supposed overlap ; and it is as fruitless to ask which of the thou- 

 sands of lofty gneiss-mountains on the east reposes on a basis of 

 these so-called older rocks. Such a thorough diversity in this step 

 in the series from all those that precede, and from all the known 

 relations of overlying beds in other countries, proves that here no 

 such overlap takes place. 



Second. The diversity in the strata brought into contact with 

 the eastern gneiss proves that the line of junction is along a fault, 

 and not one of conformable upward succession. Where a series of 



