546 Geological Society: — 



mylonitized rocks reets on the relatively unmoved sandstones. 

 Besides sandstone, this crushed mass contains abundant debris of 

 Cambrian limestone, chiefly towards the base, and resting immedi- 

 ately 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 eff'ect 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 len tides 

 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 ultrabasic, rock-debris. The hetero- 

 geneous composition thus imparted has, with flowing movement, 

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

 rocks, probably gabbros originally, have contributed more directly 

 to the composition of the complex, namely, as bands or lenticles 

 of rocks, now hornblendic, representing distinct intrusions enveloped 

 and modified by the later and more voluminous invasion of acid 

 magma. 



The chief conclusions which the author wishes to establish are : — 



(i) That the highly disturbed region of the North- West Highlands, 

 already known to extend into the south-eastern part of Skye, is 

 further prolonged into the Isle of Rum. 



(ii) That at numerous places along the disturbed belt which 

 borders the principal mountain-group of the island, the Tertiary 

 plutonic intrusions assume the character of well-banded gneisses, 

 comprising alternations of different lithological types. 



(iii) That these complex gneisses were formed mainly by fluxion 

 in a heterogeneous mass, the heterogeneity being due to the 

 inclusion and incorporation in a granitic magma of relics of ultrabasic 

 and basic rocks. 



March 25th, 1903.— Prof. Charles Lapworth, LL.D., P.E.S., 

 President, in the Chair. 



The following communications were read : — 



1. ' On a New Species oi Solenopsis from the Pendleside Series 

 of Hodder Place, Stonyhurst (Lancashire).' By Wheelton Hind, 

 M.D., P.E.C.S., F.G.S. 



2. ' Note on some Dictyonema-like Organisms from the Pendleside 

 Series of Pendle Hill and Poolvash.' By Wheelton Hind, M.D., 

 F.R.C.S., F.G.S. 



3. 'The Geology of the Tintagel and Davidstow District (Northern 

 Cornwall).' By John Parkinson, Esq., F.G.S. 



The country described and mapped consists of some 22 square 



