270 ME. W. It. WATT 01* THE GEOLOGY [June 1914, 



East of the picritic type occurs the troctolite, which shows 

 beautiful fluxion-banding. This is well seen in Craighead Quarry — 

 with a similar dip — and at Lower Sinsharnie. Still farther east 

 is found olivine-gabbro, adjoining the norite in both the Dun- 

 bennan and the Bin-Hill areas. Fine olivine-gabbros also occur, 

 but between troctolite and picrite, near Cairnford Bridge, and 

 west of Dunbennan Wood, where they form crags. 



Having regard to the dip of foliation in the surrounding 

 crystalline rocks, it becomes evident that these basic types of the 

 post-foliation intrusion are grouped along the lower margin of the 

 sill, as if differentiation had taken place under the influence of 

 gravity. 



(b) The central intrusion. — The second great intrusive 

 mass extends northwards from Broomhillock. Although having 

 in part the composition of a norite, especially at its margin, 

 it is clearly later than and intrusive into the norite already 

 described, as contact-metamorphism occurs in the latter at the 

 junction. The marginal facies of this intrusion shows slight 

 mineral banding, probably due to injection, and is extremely fine- 

 grained, as if it had been intruded when the norite was cooled. 

 As it is composed of hypersthene and plagioclase, its brown colour 

 and the parallel arrangement of its constituents serve to distin- 

 guish it from the bluish fine-grained type of the earlier intrusion. 



Within this margin, and found mainly in the southern part of 

 the intrusive mass, occurs a coarse non-foliated rock composed 

 chiefly of biotite and felspar. The central and eastern portions of 

 the mass consist of a peculiar rock possessing large garnets, in 

 addition to the felspar and biotite. This rock is referred to as a 

 garnetiferous monzonite, using the term monzonite in the 

 sense in which it is employed by Prof. Brogger. 



The distinct types found in this central massif are probably parts 

 of one and the same intrusion. No sign of any contact-metamor- 

 phism of one by the other was observed, and it is thought that, if 

 the overlying contact-altered norite on the east were removed, 

 a somewhat symmetrical arrangement about the monzonite 

 type might be observed. What is possibly a further modification 

 of this type is found in Cormalet Hill, where a normal diorite 

 occurs, likewise intrusive into the earlier norite and into the 

 crystalline schists. 



(c) The Carvichen Grranitite. — The third main intrusion 

 occurs in the extreme south-east of the area, and is known as the 

 Carvichen Granitite. In the ' gravel-pit ' on Cairnhill it is seen 

 as a decomposed coarse ' sand ' beneath the cap of hornfelsed 

 phyllites that form the summit of the hill. The main exposures 

 are found in the quarries near Carvichen, but near Corsiestane an 

 abandoned pit occurs close to garnetiferous grits. Many years ago, 

 a quarry was worked opposite Lintmill, on the right-hand side of 

 the Bogie. 



