68 MR. A. GEIKIE ON THE AGE OE THE 



would obviously be premature. It is quite certain, however, that 

 several well-marked groups occur in the deposit. What seemed to 

 me to be the lower members of the series consist chiefly of lead-grey 

 and dark mottled limestones, some of them full of the dark worm- 

 casts above referred to, others crowded with nodules and nodular 

 layers of chert. These lower beds cover by far the larger part of 

 the district. They are succeeded by massive white limestones of 

 greater pui'ity and without the abundant dark cherts. These beds 

 are best exposed at Torrin, where they form a group of conspicuous 

 hills between the base of Ben Dearg and the head of Loch Slapin. 



Comparing the Strath limestones with the similar rocks of 

 Sutherland and Ross, in which the order of succession has been so 

 well established, it is impossible not to be struck with their general 

 resemblance to the lower members of the Durness and Assynt 

 series. The dark limestones of Strath, with their abundant worm- 

 casts and cherts, recall the basal or " Grudie group" of Sutherland, 

 while the white limestones remind one of the " Eilean Dubh 

 group." I do not, of course, at present insist on these identifications 

 with particular zones in the northern Lower Silurian formations. 

 It is enough for my purpose to point out the close resemblance in 

 lithological and stratigraphical characters between the limestones of 

 Strath and Sutherland. 



Another fact which links the Skye rocks with those of the north- 

 west Highlands is the association of white quartzite with the 

 limestone. Unfortunately the way in which the latter has been 

 jumbled prevents the relations of the two rocks from being satis- 

 factorily determined in Strath. But that the quartzite underlies 

 the limestone, and is a continuation of the same quartzite which 

 can be traced from Skye continuously northwards to the far 

 headlands of Sutherland, can hardly be doubted. An interesting 

 section at Torr Mor, on the north shore of Loch Eishort, proves the 

 relation of this quartzite to the red (Cambrian or Torridon) sand- 

 stone (fig. 1). 



Fig. 1. — Section at Torr Mor, Boreraig, Loch Eishort. 



a. Cambrian (Torridon Sandstone), h. Quartzite. c. Fault, d. Lias Lime- 

 stones with pebbles of quartzite, chert, &c. e. Limestones and shales 

 with abundant Gryphcea, &c. /. Dyke of felsite. g. Overlying sheet 

 of granophyre. 



On the shore a marked fault separates the two rocks, but on the 

 hill-side above the quartzite with its usual conglomeratic base is 

 seen to lie upon the edges of the red sandstone beds. On the 



