16 MONOGRAPH OF DURA DEN. 



the cLark rugged mountains that surround Loch Goyle, Loch 

 Fyne, and Loch Awe. The hills of this formation are among 

 the loftiest and most notable in the Grampian range, rising to 

 4000 feet and upwards ; as Cairnwell, Ben-y-gloe, Schiehallion, 

 Ben Lawers, Ben Vorlich, Ben Ledi, Ben Venue, Ben Lomond, 

 and all the bold serrated ridges to the west. The lono; head- 

 land terminating in the Mull of Cantjre, great part of the 

 islands of Bute, x\rran, Jura, Isla, and the whole of Colonsay, 

 consist of mica- slate. 



Quartz- ROCK exists as an independent member of the series, 

 as well as an ingredient in every one of the primary, and of 

 nearly all other rocks. One set of theorists regard it as only 

 an altered sandstone, which, through the intense action of heat, 

 has been fused, and on cooling was crystallized. The more 

 prevailing opinion is that which ascribes it, like gneiss and 

 mica-schist, to precipitation in water ; but as it alternates with 

 both, sometimes resting on the granite, sometimes intermediate 

 betwixt the gneiss and schist, not unfrequently overlying the 

 latter, and plentifully distributed through them all, in the form 

 of veins and dykes, which penetrate, like the granite itself, the 

 whole members of the system, it is difficult to ascribe to either 

 view, and still more difficult to find a substitute for either 

 theory of formation. There are problems in every subject 

 which science has not jet solved. That there should be mys- 

 teries in geology on the formative processes of rocks, the sources 

 of their constituent elements, and their mode of aggregation, is 

 according to the rule and not the exception of speculative 

 inquiry. The quartz-rock, thus difficult in theory to be accounted 

 for, has a range and position in the Grampians nearly co-exten- 

 sive with the mica-slate, with Avhose substance it is so mixed 

 up and forms so large a proportion. 



The rock which succeeds the quartz, and sometimes alternates 

 with it, or is enclosed in its beds, is the primary limestone or 

 marble, so extensively used for ornamental purposes. This 

 formation consists of nearly equal parts of lime and carbonic 

 acid, with a trace of silica. It resembles the quartz in outward 



