236 Itejjorts and Proceedings — Geological Society of London. 



The sandstones (which are chiefly from Somaliland and the 

 south-east of Abyssinia) are sometimes compacted into quartzites, 

 and are often ferruginous. Some of the limestones are concretionary, 

 others are dolomitic, and several from different localities are fossil- 

 iferous, containing foi'aminifera, calcai'eous algge, and, at Jigjiga 

 Pass (which leads into Abyssinia), Tiirritellce in great numbers. 



The numerous specimens of volcanic rocks include one which is 

 practically a limburgite, many basalts (a few with olivine, and some 

 glassy), various less basic volcanic rocks, and several pumiceous 

 tuffs. But the most interesting are the phonolites and allied rocks, 

 containing nepheline, riebeckite, or other alkaline minerals. They 

 occur at several places, one being a volcanic hill with a summit- 

 ci'ater. The authoress distinguishes several types among these 

 soda-bearing rocks, and compares two of them with rocks of Central 

 Abyssinia and of British East Africa respectively. Thus the 

 specimens here described may form a connecting link between the 

 volcanic rocks of other East African localities. 



2. " The Overthrust Torridonian Eocks of the Isle of Eum and 

 the Associated Gneisses." By Alfred Harker, Esq., M.A., F.R.S., 

 F.G.S. (Communicated by permission of the Director of H.M. 

 Geological Survey.) 



The Torridonian strata of Eum occupy all the northern part of the 

 island, together with a strip extending along the eastern coast, the 

 high ground in the south being made by plutonic rocks of Tertiary 

 age. The northern tract consists in general of sandstones having a 

 moderate dip to the north-west or west-north-west, and below these 

 there emerges on the east side a lower group composed of dark 

 shales. There are, however, two districts in w^hich the strata are 

 highly disturbed and overthrust. One is a small area to the north- 

 w^est, on Monadh Dubh, where a cake of thoroughly brecciated and 

 mylonitized rocks rests on the relatively unmoved sandstones. 

 Besides sandstone, this crushed mass contains abundant debris of 

 Cambrian limestone, chiefly towards the base, and resting immediately 

 upon the surface of overthrust. The limestone does not occur in 

 place on the island. 



The other and more extensive area of overthrust rocks forms 

 a belt along the north-eastern and eastern border of the mountain 

 tract. The efiect of the displacement has been to bring the shales 

 of the lower group to rest on the sandstones of the upper. Above 

 the main surface of movement the shales are violently contorted, 

 and the sandstones, where these occur, brecciated. There is also 

 considerable thermal metamorphism, due to the Tertiary intrusions. 

 At numerous places along the disturbed belt are patches and lenticles 

 of gneiss. These are intrusive in the Torridonian rocks, and the 

 evidence points to their being of Tertiary age. They have arisen 

 in great part from a granitic magma modified in varying degree by 

 dissolving basic, and often ultra-basic, rock-debris. The hetero- 

 geneous composition thus imparted has, with flowing movement, 

 resulted in a well-marked gneissic banding. In a minor degree basic 

 rocks, probably gabbros originally, have contributed more directly 



