Crystalline Schists of the Malvern Hills. 147 



as the conversion of chlorite into biotite — had since been confirmed 

 by independent investigators. He held that, as a whole, the 

 gneisses and schists of Malvern had been formed by the crushing 

 and shearing of consolidated igneous rocks ; but he did not deny the 

 possibility that here and there the foliated structure might have been 

 produced in a fused mass. In the first stage of metamorphism the 

 diorite or granite was crushed and decomposed. This slightly com- 

 pressed rock could be traced step by step into a typical gneiss or 

 schist. The signs of pressure progressively increased, and the 

 mineral and chemical changes became proportionately greater. 

 Reconstruction set in. The process of metamorphism did not 

 always follow the same lines. Felspar was sometimes crushed 

 into seams of fragments, and these, by partial re-fusion and pres- 

 sure, were converted into gneissose lenticles of quartz and felspar. 

 Intervening chlorite was changed to biotite, or even to muscovite or 

 sericite. Thus a typical gneiss, consisting of quartz -felspar lenticles 

 in a felt-work of mica, was formed out of a diorite. Sometimes the 

 felspar was reconstituted without becoming fragmental ; and it was 

 then deposited on, or it included, idiomorphic mica. Or a soda-lime 

 felspar might, by a process of corrosion, be converted into quartz, or 

 a soda-felspar, or both. 



In an early stage of metamorphism, the rock was often dirty and 

 rotten through the abundance of chlorite and disseminated iron- 

 oxide. The former being changed to mica, and the latter being 

 either absorbed in the production of biotite, or reconstituted in a 

 crystalline form, a sound clear gneiss was the result. In the com- 

 pleted product, the signs of crushing and shearing were often en- 

 tirely wanting. Even strain-shadows were rare in it. The meta- 

 morphism, however, was demonstrated in numerous localities by 

 tracing the gradations inch by inch, and by the subsequent si,udy of 

 large numbers of microscopic slides, in which the transition was 

 still more clearly seen than in the field. 



The classification of the Malvern schists originally proposed was 

 somewhat enlarged, the injection-schists being subdivided into 

 (1) Schists of Primary Injection, in which one rock was injected 

 into another, and (2) Schists of Secondary Injection, formed by the 

 infiltration of secondary minerals along shear-planes. 



One of the most important of the chemical changes produced in 

 the conversion of a diorite into an acidic schist was the elimination 

 of magnesia. This was proved by analyses. The recent researches 

 of Mr. Alexander Johnstone had shown that even in the laboratory, 

 and at the ordinary temperatures, carbonated waters were able to 

 remove magnesia from certain of its combinations with silica. 



2. " Supplementary Notes on the Metamorphic Rocks around the 

 Shap Granite." By Alfred Harker, Esq., M.A., E.G.S., and J. E. 

 Marr, Esq., M.A., E.R.S., Sec.G.S. 



This paper contains some additions and corrections to the work 

 submitted to the Society by the authors on a previous occasion 

 (see Quart. Journ. Geol. Soc. vol. xlvii. p. 266). In the present 



