Dr. C. Callmoay- — Schist-making in the Maherns. 545 



IV. — Notes on the Process of Schist-making in the Malvern 



Hills. 

 By Chakles Callaway, D.Sc, M.A., F.G.S. 



IN the October Number of this Magazine, a paper by the Kev. A- 

 Irving, D.Sc, calls for some comment. The subject, " The 

 Malvern Crystallines," is one which has engaged my close attention 

 during the last seven years, and two expositions of my views have 

 appeared in the Quarterly Journal of the Geological Society.^ I am 

 glad to find that Dr. Irving accepts my main conclusion — that the 

 Malvern gneisses and schists are of igneous origin ; but there are 

 some important details in which he has formed a diiferent opinion. 

 It will not be necessary for me to discuss these differences with any 

 fulness, since my third and final paper, which is nearly ready, treats 

 of some of his more material objections to my views. 



One of the most important points of difference is the origin of the 

 granite-veins. I hold that they are injected into the diorites, and 

 therefore posterior in age ; Dr. Irving regards them as segregatory 

 and contemporaneous. I notice, with some surprise, that Dr. Irving 

 quotes the late Prof. John Phillips in support of his theory. The 

 words of the Oxford Professor, as recorded in the " Geology of 

 Oxford and Valley of the Thames," appear to me to contradict his 

 claim. Writing on the granites, diorites, and other crystalline rocks 

 of Malvern, Phillips says (p. G2) : — " Segregation from a fused mass 

 is often regarded as the cause of these irregular mixtures ; in several 

 cases, however, the posteriority of felspathic and granitic veins to 

 the masses which they traverse is quite certain. . . ." 



Dr. Irving contends for the segregatory and contemporaneous 

 origin of the granite-veins on the following grounds : 



(1) Upon the way in which the diorite and the granite " graduate 

 into one another ; " and he alleges a case at West Malvern of a 

 " gradation from diorite through a biotite or hornblendic-granite 

 to a very coarse pegmatite." 



My experience upon this point lends no support whatever to this 

 alleged graduating. There are few outcrops in the Malvern range 

 ■which I have not examined, and I have never succeeded in finding 

 a passage between granite and diorite. On the other hand, I have 

 observed hundreds of contacts between those two rocks, in which 

 they were seen to be sharply distinguished from each other, and I 

 have examined scores of these contacts under the microscope with 

 the same result. The supposed "gradation" at West Malvern is 

 probably a case of the action of granite on diorite in contact, of 

 which there are plenty of examples in that locality. 



(2) "Upon the way in which the felspathic and the quartzo- 

 felspathic veins ramify in all directions through the diorite." 



This might sometimes be the case if the granite was ejected from 

 below. The molten rock would pass along lines of least resistance, 

 which would sometimes be horizontal or even trend obliquely down- 

 wards. As a matter of fact, however, a large proportion of the veins 

 1 August, 1887, p. 525 ; August, 1889, p. 475. 



DECADE III. — VOL. IX. — NO. XII. 35 



