560 HISTORY OF THE OUTER HEBRIDES. 



Macculloch's, this deposit had been put down on Knipe's 

 Geological Map as Old Red, with a note, however, that 

 Murchison had called in question this belief, and had 

 stated, at a meeting of the British Association, held at 

 Leeds on September 28th, 1858, that his opinion was that 

 the whole of the sedimentary rocks in the north-west, from 

 Cape Wrath to Sleat in Skye, were Cambrian. That 

 opinion has been accepted by Geikie ; but in these days of 

 " obstinate questionings, blank misgivings," that opinion is 

 itself called in question. 



Whatever opinion he held regarding the age of the 

 Torridon Sandstone whether it be of Cambrian or of 

 Precambrian Age my proposition is that the Lewis 

 Conglomerate has been connected with that sandstone on 

 inadequate grounds. 



Heddle, in his Geognosy of Scotland, Part I 

 41 Sutherland," conclusively shows that the Torrid 

 Sandstone grits or Conglomerates are not, as Murchi 

 supposed they were, " made up exclusively of the gneiss 

 on which they rest." Heddle shows that the marked 

 absence of hornblende from the Torridon formation an 

 absence remarked also by Macculloch, Cunningham, 

 Nicol, and Professor Bonney is a difficulty not to 

 be surmounted by Murchison's view. True, as Heddle 

 admits, that he is not in a position to deny that 

 this many-bedded formation is in some part formed 

 of the ruins of the underlying gneiss ; yet the total 

 absence, or almost total absence of hornblende, and the 

 presence, on the other hand, of the very " large amount of 

 fine-grained porphyries, and especially of colloidal silica 

 as seen in jaspers, cherts, and vein-hornstones which goes 

 to form its pebbles," point to some other than the presently 

 remaining Archaean rocks as the parent source of these 

 sandstones, grits, and conglomerates. Dr. Hicks, quoted 

 by Heddle, points out that the presence of bits of greenish, 

 purplish, and reddish slates, jasper, &c., in these Con- 

 glomerates, makes it quite possible that in some other 

 area, not far distant, representatives of these Precambrian 



