452 Dr. Irving — The Malvern Crystallines. 



V. — The Malvern Crtstallines.^ 

 By the Eev. A. Irving, D.Sc, B.A., F.G.S. 



THE author having made an examination in the field of the 

 Malvern Crystallines, during a residence of ten weeks at 

 Malvern in the early part of the year, and having had the advantage 

 of Dr. Callaway's company over portions of the ground towards the 

 end of the time, offers here an outline of his observations and the 

 general conclusions to which his field-work has led him, reserving, 

 for the present, all details of microscopic work. 



I. He agrees with Dr. Callaway^ (with one doubtful exception) 

 that the whole crystalline mass, from end to end, is of igneous origin, 

 but cannot follow that observer in regarding the granites as injected 

 into the diorites (the " syenites" of Phillips and HoU). The author's 

 observations rather lead him to doubt if any true sequence can be 

 made out between these two rocks (using the terms in a broad 

 generic sense), the observed phenomena seeming to square better 

 with the view, which would regard them as segregation-products of 

 "one original unerupted magma," as was suggested more than forty 

 j^ears ago by the late Professor J. Phillips, F.R.S.^ (see Mem. Geol. 

 Survey, vol. ii.) ; and he regards the coarse pegmatitic varieties of 

 granite (the "binary granite" of Callaway) as the siliceous residnum 

 of the magma, after the whole (or nearly the tohole) of the silicates of 

 the heavier bases had crystallized out ; * applying this even to such 

 a coarsely-crystalline mass as may be seen on the top of Worcester 

 Beacon, where one mass of individualized quartz was observed nearly 

 a foot thick. ^ He bases this view on such facts as the following : — 



Istly. Upon the way in which the dioritic and the granitic rocks of 

 the chain graduate into one another (as in Worcester Beacon and 

 North Hill), or alternate with one another (as in the Swinyard Hill); 



^ A paper read before Section C. of the British Assoc, Edinburgh meeting, 1892. 



- See the two able papers by that author in the Q.J.G.S. for 1887 and 1889. 



^ Even at that early date Phillips had as clear an idea of the differentiation of 

 a homogeneous fused mass into a heterogeneous crystalline mass' as a recent writer 

 in " jNatural Science" (Jime, 189'2), whose application of the theory of "osmotic 

 pressure " (as applied to " dilute solutions "), to help him to construct a "sequence 

 of plutonic rocks'' (a theory which can hardly be said as yet to have established 

 itself in Chemical Physics) seems rather strained. Durocher's principle of " liqua- 

 tiou" is probably nearer the truth. But as different physical conditions (chiefly 

 temperature and pressure) determine the allotropes of one and the same chemical 

 body, so they undoubtedly are large determining factors of the order of crystalliza- 

 tion of minerals out of a given magma, and the consequent composition and 

 critical temperature of the residual magma at any stage of rock geneisis. It is hardly 

 necessary to state, that with much that is contained in the article referred to the 

 present writer entirely agrees. 



* The fact that most of the felspar in the Malverns turns out to be plagioclase 

 (carrying over many of the " syenites " of the earlier writers to the diorites) is in 

 favour of this view; since "soda, weight for weight, fluxes more than potash ;' 

 and ' ' lime may produce, with a great number of infusible, or slightly fusible, 

 silicates, compounds which melt easily." (Percy, "Fuel, etc." London, John 

 Murray, 1875, pp. 73, 7o). 



* Individual hornbleudes, comparable for size with these, were not met 'with in 

 the field, but some may be seen in the Museum at Malvern College. 



