34 MIDDLEMISS : THE GEOLOGY OF IDAR STATE. 



sian magmatic material bad been too complex in its composition 

 to favour the formation of any simple mineral species. Thus, 

 examined microscopically, the dark minerals, though generally green 

 pyroxene and its uralitic derivatives, are often biotite or garnet or 

 groups of these together ; whilst in special cases, and less frequently, 

 appear zoisite, epidote, sphene, tourmaline and allanite. Notwith- 

 standing these differences, the veins being too small to map, are 

 also too small to subdivide further on the ground, especially since 

 their differences of composition are often merged in a general 

 superficial likeness. Whether these differences vanish by local 

 passages or not cannot be certified on the present data at my dis- 

 posal. In the. country south of Khed Brahma it is not unlikely 

 that the pyroxene-aplite is in a measure distinct from the biotite- 

 aplite which occasionally develops tourmaline at the edges, a 

 difference that is paralleled by the varying bands of the calc-gneiss, 

 some of which as we have seen, are characterised by green diopside 

 and some by biotite being in the ascendancy. 



Without necessarily implying any important genetic distinctions 



between the different varieties of these vein 

 Classification, ... ,. . . x1 1 •/: j 



aphtes, they may be conveniently classined 

 as granite aplites and syenite aplites (from the point of view of the 

 white minerals) and as biotite aplites and pyroxene-hornblende 

 aplites (from the point of view of the dark minerals). Even then a 

 few varieties would remain over, such as those with garnet or with 

 allanite as the sole dark minerals, and a few consisting of a coarse 

 graphic intergrowth of quartz and felspar without any dark minerals 

 at all. 



A characteristic of all these differentiated hypabvssal rocks 

 is the practical absence of all free iron-ores in their composition 

 as has also been seen to be the case in the calc- and other gneisses. 

 Another negative characteristic is that they never appear as very 

 coarse-grained pegmatites (giant granites) with very large crystal- 

 line elements or, so far as at present detected, important occur- 

 rences of valuable minerals. The following examples, which are 

 illustrative and not exhaustive, will sufficiently describe these 

 veins. 



Granite Aplites. 



Certain of these aplite veins (which, as already remarked, could 

 not be separately mapped on the scale of the present survey) are 



