CRYSTALLINE .SERIES. 



13 



limestone or may represent apophyses from the granite. The band of 

 pyroxene granulite is only about two inches thick and passes away into 

 limestone on one side and granite and schist on the other ; it contains a 

 great deal of sphene and has all the appearance of a contact product 

 due to the interaction of the granite and the limestone. The develop- 

 ment of the numerous accessory minerals in the limestone is clearly due 

 to the effect of the intrusion of the granite, since these minerals are always 

 most numerous at the junction of the two rocks. The most highly 

 mineralised parts of the limestone are, in fact, associated with narrow 

 ribbons — two or three inches thick — of decomposed rock consisting chiefly 

 of quartz, felspar and biotite ; these might be called either biotite-gneiss 

 or biotite-schist, and appear to be apophyses from the foliated augen 

 gneiss — originally a granite— which is intimately infolded with the 

 crystalline limestone. 



To the south, the limestone belt is succeeded by the schists already 

 referred to (supra, p. 11) and which appear at one time to overlie, at 

 another to underlie, the limestone. These again give place to a belt of 

 pegmatite, which is younger than the schists. It is of the ordinary 

 Himalayan type and is composed of quartz, felspar, muscovite (in fairly 

 large crystals), some schorl and beryl. The pegmatite band is about 

 100 yards wide where it was crossed by me : it appears to run eastwards 

 for miles along the Siah Koh approximately parallel to the strike of 

 the schists and crystalline limestone. To the south of this pegma- 

 tite, another limestone series occurs and probably forms much of the high 

 ranges between the Jagdallak ruby mines and Surkhpul. In the 

 immediate neighbourhood of the pegmatite it occurs in thin flags at first 

 white, then — a little further off — yellowish and ferruginous ; still further 

 away it is grey and occurs in thicker beds associated with phyllite and 

 quartzite. The grey limestone contains small patches of calcite and 

 occasionally streaks of hematite. This limestone series is quite different 

 in appearance to, and much less highly metamorphosed than, the miner- 

 alised crystalline limestone described above ; it is, however, schistose 

 and distinctly metamorphic. 



