38 Notices of Memoirs — Geikie 8^ Flett — Ayrshire Granite. 



Mr. T. A. Falcon on Loch Coruisk, show that it occupies an area 

 of two rock-basins, which have been excavated by ice-action. 



Evidence is brought forward to show that succeeding the great 

 glaciation there was a minor glaciation due to the action of glaciers 

 occupying the valleys, at a time when the obstruction caused by 

 the Scottish ice-sheet had been removed, and when the Skye ice 

 was free to follow a course more in accordance with local topography. 

 The author observes that the distribution of the cirques suggests 

 a connection with the direction of sunshine ; that the asymmetric 

 character of the ridges and valleys in the outer parts of the mountain 

 area may be attributed to the different aspects of the slopes relatively 

 to the sun; and that therefore this influence was exerted, not at 

 the time of maximum glaciation, but when the ice-cap had shrunk 

 so as to occupy the valleys alone, and during the later glaciation, 

 which was effected by glaciers only. He has not attempted in all 

 cases to apportion the work of erosion between the ice-cap and the 

 glaciers. His further detailed observations on the drift deposits, 

 on the distribution of boulders, on perched blocks, and on the 

 formation of screes will be read with profit. They furnish evidence 

 of his careful methods of research, and of the impartial way in 

 which on all occasions he interprets the facts. 



II. — The Granite of Tullogh Burn, Ayrshire. By Professor 

 James Geikie, F.K.S., and John S. Flett, M.A., D.Sc.^ 



rpHE granite of TuUoch Burn, Ayrshire, is a small mass occupying 

 JL an area of three or four square miles on the headwaters of 

 the Irvine and the Avon. Much of the outcrop is covered with 

 drift and peat, but good exposures of the granite and the contact- 

 altered rocks can be obtained in the TuUoch Burn, a tributary 

 of the Irvine, and on the Avon. The prevalent type is a flesh- 

 coloured biotite - granite, which often contains hornblende and 

 sometimes decomposed augite. This passes at its margins into 

 rocks of intermediate or basic composition, which include various 

 types of diorite, hyperite, and gabbro. The evidence points to the 

 origin of these rocks by a process of differentiation, and both in 

 this respect and in the rock species vi^hich have been developed 

 the resemblance to the granites of the Southern Uplands is very 

 close. The material microscopically examined includes — Graphic 

 Granite and Granophyric Granite (in segregation veins) ; Biotite 

 Granite, Biotite Hornblende Granite, Biotite Augite Granite ; 

 Tonalite (intermediate between Hornblende Biotite Granite and 

 Diorite) ; Quartz Hornblende Diorite, Quartz Augite Biotite Diorite, 

 Quartz Hypersthene Diorite ; Biotite Augite Diorite, Hornblende 

 Diorite, Hypersthene Diorite ; Hyperite and Gabbro. 



This mass is intrusive into the Lower Old Eed Sandstone, which 

 at Lanfine, a little west of this, has yielded Cephalaspis Lyelli. The 

 Old Eed Sandstone is indurated and often hornfelsed to a varying 

 distance from the margin. The new minerals developed are Augite, 



^ Eead before the British Association, Section C (Geology), Glasgow, Sept., 1901. 



