362 SANDSTONE, MARBLE AND QUARTZ DEPOSITS. 
fossiliferous rocks cannot be traced, we must, I suspect, be con- 
tent with simply the probable. For my own part, the occur- 
rence in one of the flagstones of Strongchrubie, of the spine 
of a Cheiracanthus, or of a few scales of Dipterus, or of the 
plates of a Coccosteus, would satisfy me more thoroughly than 
all the arguments ever derived from mineralogical character, 
or from the occurrence, in a certain order, of certain peculiarly 
marked beds. But while I must regard the identity of the 
Red Sandstone of the north-eastern and north-western coasts 
of Scotland as by no means fully established, I am at least 
strongly of opinion that, as they are essentially the same in their 
aspect, order, and components, they represent also the same 
period in the history of the globe. From finding the strata of 
the Old Red Sandstone upturned against our primary moun- 
tains, and truncated atop, and from those detached fragments 
of the system which occur as insulated hills far in the High- 
land interior, I was led to conclude, many years ago, that this 
deposit had at one time overlaid all the primary rocks of 
Scotland, from the southern flanks of the Grampians to the 
northern boundary of Sutherland,—a conclusion to which 
Sir Charles Lyell, in the later editions of his “ Elements,” has 
approvingly referred, as coincident with views on the subject 
entertained by himself. And these arenaceous rocks of 
Assynt, with their associated limestones and marbles, I must 
regard as in all probability a portion of this once continuous 
system, hardened by metamorphic action, and which having, in 
consequence, resisted the denuding agencies that swept away 
the contemporary beds, still continue to wrap over the con- 
torted and broken gneisses and granites of the district, and to 
form its most elevated mountains. ‘It is the surviving frag- 
ment of a covering of which almost all the other portions have 
crumbled away piecemeal and disappeared. 
