392 C. CALLAWAY ON THE NEWER GNEISSIC 



We now come to the section on the north side of the valley. Leaving 

 the shepherd's house on the shore of the loch, and ascending the 

 glen, we pass over Hebridean with N.N.W. strike, which is con- 

 tinued, with few exceptions, up to the Quartzite. A few feet below 

 the Quartzite the gneiss becomes rotten, and changes to the dip of 

 the former. The Quartzite has at its base a band of red felspathic 

 grit, and encloses red felspar bits. It dips steadily up the glen for 

 some distance ; then, when it becomes overhung by the Caledonian, 

 it is squeezed up into a series of small folds thrown over to the 

 N.W. The most easterly of these are on the strike of the overthrown 

 fold on the opposite side. A little further east, the Caledonian comes 

 down to the stream, the bed of which is occupied by the Hebridean. 

 The ground just here is masked by talus of newer gneiss, so that 

 no junction can be seen ; but the lowest visible Caledonian is within 

 50 feet vertically above the Hebridean ; and continuing with the eye 

 the strike of the Caledonian across the glen, it seems as if it must 

 actually touch the Hebridean. This is confirmed by taking the 

 heights with the aneroid. The Caledonian on the northern slope de- 

 scends to at least 925 ft., while the Hebridean just over the stream 

 rises to 950 ft., which, allowing for the slight slope of the Caledonian 

 beds from south to north, would about correspond. Beyond this 

 point the Caledonian still descends on the dip to the east ; so that 

 the actual contact of the older and younger gneisses cannot admit of 

 doubt. Now, as the Assynt series in this locality is at least 200 ft. 

 thick, it obviously cannot pass to the east. 



I infer from the facts described, that by a reversed fault the 

 Quartzite has been broken off and crumpled up in the angle between 

 the overhanging Caledonian and the underlying Hebridean. There 

 will be little a priori difficulty in accepting this conclusion after 

 studying the enormous overthrows of the old gneiss within two miles 

 to the west. There can be no doubt that the overthrow of the Hebri- 

 dean and the reversed faulting at the junction with the Eastern 

 Gneiss are due to the same general cause. 



As the dips of the Caledonian are to E.N.E. and E. at 15°, while 

 the Hebridean dips at a high angle toN.,jN".N.E.,and sometimes N.E., 

 the unconformity between the two gneissic groups is well marked. 



F. Structure of Assynt. 



The preceding sections have anticipated much of what comes 

 under this head ; but it will not be uninstructive to bring together 

 into a connected whole the facts which throw new light upon the 

 mountain-structure of this remarkable district. 



The lofty mountains have always been justly regarded as amongst 

 the most interesting features in the scenery of Assynt. Erom a 

 distance they appear like peaks of snow ; and even on closer ex- 

 amination many of them seem to be composed of quartzite from base 

 to summit. Hence writers have supposed them to be solid masses 

 of that rock, and formations of quartzite thousands of feet thick 

 have been described. This appearance is quite illusory. The 

 quartzite is merely a sheet, about 300 feet thick, wrapping round 



