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DE. C. CALLAWAY OX THE GENESIS OF THE 



These modified felsites, now schists, form a low vertical cliff, 30 

 or 40 yards long, in which the rock is continuously exposed. I 

 worked along the strike to the western end and found similar 

 schists, some of them highly quartzose, passing occasionally into a 

 material like a quartzite, and into felsitic rock like the first named. 

 The different varieties were not always interbanded, but often passed 

 into each other with some irregularity. That they all belong to the 

 same mass I have no doubt. The rapid variations in the metamor- 

 phism agree with the sudden changes noticed in the crushed granite. 

 A specimen of one of the quartzose varieties, almost like a quartzite, 

 was examined microscopically. In structure it is intermediate 

 between a quartzite and a quartz-schist. There is very little orien- 

 tation in the quartz, which is frequently in large granules, Mica is 

 in small proportion. Much of it is in clear microliths, which 

 occasionally form a partial sheath to the quartz-granules, as in the 

 other schists of the locality, but more frequently they have a rough 

 orientation in one direction ; occasionally they accumulate into 

 imperfect folia. Parallel with this foliation are several cracks, 

 which are more or less filled in with mica and iron-oxide. Some, if 

 not most, of the mica in the cracks is the same white variety which 

 prevails throughout the slide. This parallel cracking, coincident 

 with the foliation, is another interesting analogy between this schist 

 and the crushed granite, and is of course suggestive of similarity of 

 causation. 



B. Injection-Schists, or those in which the Banded Structure is 

 due to the Parallelism of Intrusive Veins. 



Two varieties of this rock are here described. 



Duplex Diorite-gneiss, formed from veins of Diorite in Diorite. — 



This fine-banded rock is common in one of the quarries at North 

 Malvern. Parallel seams of grey granitoid diorite (No. 3) are 

 enclosed in a black variety (probably No. 1). The differences 

 between the ordinary diorites and their gneissic representatives cer- 

 tainly do not militate against my theory of the origin of the latter. 

 The following points may be noted : — 



In the massive black diorite there is some epidote and chlorite and 

 a little green biotite, but in the gneiss there is a much larger pro- 

 portion of biotite, and most of it has a definite orientation parallel 

 to the direction of the adjacent vein. Some haematite also, which 

 is in lath-shaped forms, is similarly orientated. The felspar of the 

 ordinary diorite is cloudy, rarely showing plagioclase-twinning, and 

 contains numerous clear microliths. In the gneiss the felspar of 

 this diorite is rather clearer and sometimes displays striping. 

 Comparing the unfoliated grey diorite with the grey variety in the 

 gneiss, there is no material difference observable. The crystalli- 

 zation of the latter is larger, but in both cases the felspar is pre- 

 dominantly plagioclastic, and the proportions of hornblende, biotite,. 

 epidote, and quartz are about the same. 



Owing to the want of continuous sections, I was unable to trace 



