ON THE CEYSTALLINE SCHISTS OF THE MALVERN HILLS. 



525 



.37. A Peellulnary Inquiry into the Genesis of the Crystalline 

 Schists of the Malvern Hills. By Ch. Callaway, Esq., D.Sc, 

 F.G.S. (Read April 6, 1887.) 



Introduction. 



1. The Materials from which the Schists were produced. 



Diorites, Several Varieties ; Granite ; Felsite. 



2. Evidence of Pressure. 



Contortion of Granite-veins. 



3. The Products of the Metamorphism. 



A. Simple Schists. 



Hornblende-gneiss, Mica-gneiss, Mica-schists. 



B. Injection-Schists. 



Duplex Diorite-gneiss, Granite-diorite-gneiss. 



4. General Remarks. 



5. Summary. 



Introduction. 



The igneous origin of some foliated rocks was first suggested to 

 me by the granite of Northern Donegal*. The Bev. E. Hill, 

 F.G.S., had previously noticed f a gneissic structure in the granite 

 of Guernsey. Mr. J. J. Harris Teall, F.G.S. ; has described foliation 

 in basic rocks in the North-western Highlands J and at the Lizard§. 

 Schistosity in granitoid rocks has also been observed in the Alps 

 by Professor Bonney||, F.B.S. Besides English workers, several 

 foreign writers, both American and Continental, have declared in 

 favour of an igneous origin for certain schists, so that the produc- 

 tion of a parallel structure in igneous rocks may fairly be regarded 

 as an established fact. 



The work which I have described in another paper (p. 517) led me 

 to hope that we might be able to advance a step further. The intru- 

 sion of veins of granite in diorite, under pressure, suggested that at 

 great depths, where pressures were at a maximum and chemical 

 processes might be presumed to be most active, gneissic rocks of a 

 more varied character might be produced. At the town of Galway 

 I had seen gneisses which might have been produced in this way ; 

 but the crystalline schists of the Malvern Hills have furnished clear 

 evidence of the genesis of some of the more complex gneisses, be- 

 sides throwing additional light upon the production of the simpler 

 schists. I am able to show that many of the schistose rocks of 

 Malvern have an igneous origin, and I hope that the clues I have 

 obtained will enable me in a future communication to extend my 

 explanations to certain varieties whose genesis is at present less 

 clearly ascertained. 



* Quart, Journ. Geol. Soc. vol. xli. p. 221. 



t Ibid. vol. xl. p. 404. 



X Ibid. vol. xli. p. 133. 



§ Geol. Mag., Nov. 1886, p. 481. 



|| Quart. Journ. Geol. Soc. Pres. Address, 1886. 



Q. J.G.S. No. 171. 2n 



