Geological Soc-iety of London. 28& 



phosed conglomerate " ; but the included blocks of diorite bad 

 acquired a definite orientation, apparently due to pressure. An 

 igneous origin for some of the coarser gneisses was thus suggested. 

 It was concluded that there was no proof of the conversion of schists 

 into igneous rocks, the evidence collected tending to show, on the 

 other hand, that igneous rocks were sometimes converted into schists. 



3. " A Preliminary Inquiry into the Genesis of the Crystalline 

 Schists of the Malvern Hills." By C. Callaway, Esq., D.Sc, F.G.S. 



The author's researches amongst the crystalline rocks of Con- 

 naught had suggested certain lines of investigation which had sub- 

 sequently been followed out in the Malvern district. He had satisfied 

 himself that many of the Malvern schists had been formed out of 

 igneous rocks ; but at present he limited himself to certain varieties. 



The materials from which these schists were produced were diorite 

 (several varieties), granite, and felsite. 



The metamorphism had been brought about by lateral pressure. 

 Evidence of this was seen in the intense contortion of granite-veins 

 and in the effects of crushing as observed under the microscope. 



The products of the metamorphism were divided into two 

 groups : — 



A. Simple schists, or those formed from one kind of rock. The 

 varieties described were the following : — Hornblende- gneiss, or diorite 

 which had been crushed and modified. Mica-gneiss, formed from 

 granite. In the first stage of the crushing, the quartz and felspar 

 lay in lenticular fragments, separated from each other by cracks, the 

 fragments and cracks being roughly parallel. As the metamorphism 

 proceeded, the cracks became less evident, and the respective minerals 

 were flattened out into comparatively uniform folia. Mica gradually 

 came in, at first in the form of a partial coating to felspar crystals, 

 and, at a further stage, in regular folia. Mica- schist, formed from 

 felsite. The felsite gradually acquired a parallel structure. JPari 

 passu with this mechanical alteration, a mineral change was observed. 

 Mica at first appears in very small quantity, either filling cracks or 

 accentuating the parallelism. In a more advanced stage, the mica 

 lies in imperfect folia, and sometimes forms a partial coating to 

 grains of quartz. At last there is little left but quartz and mica, 

 the latter in folia, and enveloping individual quartz granules. 



B. Injection schists, formed by the intrusion of veins, which had 

 acquired parallelism by pressure. Veins of diorite in diorite pro- 

 duced duplex diorite-gneiss, and veins of granite in diorite originated 

 granite diorite-gneiss. 



It was further noted that 



(1). Generally the particular varieties of schist occurred in the 

 vicinity of the igneous masses to which they were most nearly 

 related in mineral composition. 



(2). The mineral banding of the rocks in the field was more like 

 vein-structure than stratification. 



The author accepted the received view of the age of the schists. 

 The parallel structure was clearly antecedent to the Cambrian epoch, 

 and the occurrence of similar rocks as fragments in the Uriconian 



