Dr. C Callaway — Schist-making in the Malverns. 547 



The rock surrounding them, wherever I have seen them, is sheared 

 into a well-foliated gneiss, with well-marked granulitic structure. 

 Each " cake " forms a nucleus around which the gneissic folia are 

 arranged concentrically, and would appear to be merely a tough 

 mass which has succeeded in resisting the shearing action of the 

 earth-mill. The granulitic structin-e would of itself suggest dynamic 

 deformation subsequent to consolidation. The sheared rock was 

 originally binary granite of very coarse grain, into which it often 

 passes by imperceptible gradations, and the " eyes " can be identi- 

 fied as the same kind of granite, though they have often become 

 more highly siliceous. 



Dr. Irving does not appear to dispute that the production of biotite 

 in the diorite is sometimes the result of contact alteration ; but he 

 denies that such is always the case at Malvern, and he instances the 

 rock in the large quarry at the north-west corner of Swinyard's Hill. 

 He states that the "kersantite" shows "no progressive alteration" 

 as it approaches the " basic dykes." I should be very much sur- 

 prised if it did. My induction was that usually black mica was 

 developed in diorite at the contact with the granite-veins. It is true 

 that no granite is visible in this quarry ; but it is also true that one 

 of the largest masses of granite (pegmatite) in the Malvern Hills 

 crops out at a little distance to the east, where it forms the ridge of 

 the hill for several hundred yards. 



The sericite- schists of the south-western spur of the Eaggedstone 

 have attracted the attention of Dr. Irving. He thinks they form 

 "a fragment of the lithosphere belonging to a much later stage of 

 development than the rest of the Malvern chain," and he " failed 

 in his attempt to trace a gradual transition from them into the 

 gneissose rocks adjoining these schists." These schists are of extreme 

 interest, and will be fully discussed in my third paper. In this place 

 I may say that I have traced a "gradual transition" between them 

 and the coarse-grey diorite, and I am in a position to prove by 

 means of a series of about forty microscopic slides, cut from the 

 diorite, the schist, and the intervening rock, that this highly acidic 

 schist has been formed out of the diorite by a process of crushing 

 and shearing, acting subsequently to the intrusion of the granite-veins 

 and to the solidification of the mixed rocks. 



On the mica-schist (formed from felsite) of the south-eastern spur 

 of the Raggedstone, I have merely a word to say. Dr. Irving thinks 

 I ought not to apply the term " schist " to this rock ; but he does 

 not deny that " cleavage-foliation " is to be seen in it. If there is 

 true " cleavage-foliation " in the rock, surely it is entitled to be 

 called a "schist" in the strictest sense of the word, if the usage of 

 British geologists, from Jukes onward, is to go for anything. But 

 Dr. Irving appears to use the term "cleavage-foliation" in a peculiar 

 manner, since he compares this Eaggedstone schist with certain 

 " laminated sandstones, on the lamination surfaces of which a similar 

 deposit of secondary mica has taken place." I cannot for a moment 

 admit that such a comparison is justified by the facts. If Dr. Irving 

 will turn to my first paper (1887, p. 531), he will see that, while 



