454 Dr. Irving — The Malrern Crystallines. 



and comjiosition of parts of the same igneous intrusive mas8 

 observed years ago by Allport in some dolerites ; from tbe more 

 remarkable differentiation of parts of the same dyke in continuous 

 cross-sections described by Dr. Andrew C. Lawson, of the Canadian 

 Survey, in a paper which the author received last year from that 

 distinguished geologist (American Geologist, March, 1891, on the 

 " Petrographical Differentiation of certain Dykes in the Rainy Lake 

 Region ") ; from known cases of the derivation of basic and acid 

 rocks from the same magma in well explored volcanic foci ; ^ and 

 from the fact that he has himself found the Bronsill intrusive 

 dolerite (near Eastnor) pass into an almost pure pegmatite in one 

 part. Even where such a rock occurs as kersantite or mica-diorite, 

 there is not always evidence to point to contact-alteration as the 

 origin of the mica. It seems easier to regard this rather as a primary 

 mineral constituent of the rock in places ^ .(mica taking the place of 

 the hornl)Iende of the prevalent diorite) ; for in one place (West 

 Malvern) the kersantite seemed to vein the adjacent rock, while in 

 the greatest exposure of kersantite seen in the Malvern Range it was 

 intersected by basic dykes, unmistakably intrusive, and no other 

 acid rock was exposed. This was in the quarry at the north-west 

 corner of Swinyard Hill, where no progressive alteration could 

 be observed macroscopically in the kersantite as it approached the 

 basic dykes. 



II. The only intrusive rocks the author has been able to recognize 

 from end to end of the chain are (a) feJsites, becoming at times 

 qnartz-porphyry ; and (b) dolerites of different varieties, including 

 diabases. 



The felsitic dijhes contain occasionally inclusions of a basic rock 

 (probably diorite altered by contact), and are very well seen at 

 North Malvern, at Gold Hill north of the Wych (porphyritic), 

 about Wind's Point, in the Raggedstone Hill (as described by 

 Dr. Callaway), and in other localities. 



The dolerites are much more common, and enter much more 

 largely into the geotectonic structure of the range, being met with 

 from end to end of it. They are often aphanitic in texture, and 

 in a great proportion of instances have undergone in part intense 

 crushing in the subsequent mountain-building stage of the history 

 of the region, with re-cementation into a solid breccia. Many 

 of the boklest crags consist of these rocks (North Hill and in 

 Rashy Vallej' above Great Malvern). In all such cases a special 

 point was made by the author (in the light of experience gained 

 in former years in the Eifel, in the Bozen country, in the Neapolitan 

 region, in Charnwood Forest and in Snowdonia) of searching for 

 evidence of tvffs, but without finding anjf, although one or two 



1 See in particular the very instructive instances described by Crednet {Elemente 

 dcr Geologie, sixth edition, page 587) at Preduzzo and Monzoni, in the Italian Tyrol. 



- To contend that the mica of kersantite is always a secondary mineral would land 

 us in the difficulty of having to recognise it as such (by " endogenous " alteration) in 

 eases where kersantite occurs as an mtrusire mck, as for examples in the Devonian 

 and Carboniferous of the Hartz region, and in the Culm of Lower Silesia (Credner, 

 op. cit. pp. 464, 500). 



I 



