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



are seen to rii?e from below, thinning out upwards and often forking 

 (see fig. 2, p. 482, Quart. Journ. Geol. Soc. August, 1889). For 

 one vein that runs horizontally, there are perhaps a hundred that are 

 almost vertical. 



(3) "Upon the fact that very often the hornblendic rock is 

 observed to be more completely basic in immediate contiguity with 

 the felspathic veins." 



It is true that sometimes there is an aggregation of hoi-nblende or 

 biotite forming a rim to the diorite at the junction with a granite- 

 vein, as I pointed out in 1889 (loc. cii. p. 494) ; but I hold this to 

 be the effect of the injection of the granite, by which a process of 

 mineral aggregation and enlargement is originated, as had been noticed 

 in other localities by Allport, Bonney, and others. Dr. Irving's theory 

 of these basic rims does not explain why, when the hornblende (or 

 liiotite) is segregated from the felspar, it should leave on one side 

 of it a band of plagioclase (mainly), and on the other a band which 

 is chiefly orthoclase and quartz. The segregation of hornblende 

 from felspar has, indeed, often taken place in the Malvern diorites, 

 but, so far as I have seen, the felspar remains mainly diorite-felspar, 

 viz. plagioclase. 



(4) '• Upon the very significant fact, that the quartzo-felspathic 

 veins, even when less than an inch in thickness, have a coarsely- 

 grained structure, this being so manifest as to make it impossible 

 to believe that they crystallized in contact with a colder rock after 

 injection into it." 



Dr. Irving is justified in attaching importance to this argument. 

 If it stood alone, it would have great weight. But the facts making 

 in the opposite direction are so strong [loc. cit. pp. 494, 495) that 

 I think it will not do to attach much value to a fact which may be 

 susceptible of another interpretation. It is likely enough that when 

 the veins were injected, the diorite was at nearly as high a tempera- 

 ture as the granite, so that the veins maj' have cooled down nearly 

 as slowly as the large masses of granite with which they were in 

 connection. For my part, I find it incredible that masses of potash- 

 granite, hundreds of yards in diameter, should have segregated out 

 of the diorite, that the segregated matter should be as coarsely 

 crystalline in fine-grained diorite as in the granitoid variety, and 

 that veins of segregation should produce the same contact-effects as 

 veins of injection. 



A second important detail is whether scMstosiiy loas produced hefore 

 or after consolidation. Speaking generally. Dr. Irving says, "before." 

 Speaking generally, I say, " after." The reasons for my view are 

 given in part in my second paper, and will be continued in my next. 

 I confine myself in this article to a brief reference to the "cakes" 

 of quartz or quartz-felspar which occur in some of the more felspathic 

 masses. Dr. Irving supposes that this flattening out into " cakes " 

 took place when the quartz was in a colloid state. I select this case 

 because it may seem to be a strong point in his favour. There is, 

 however, pretty clear evidence that these "cakes" ai*e merely very 

 large "eyes," such as occur on a smaller scale in augen-gneiss. 



