LADAKH, NORTH-WESTERN HIMALAYA. 325 



and zoisite are often intimately associated together. In the case of 

 the rock under consideration, I think it probable that the hornblende 

 was derived by paramorphic change from augite. On this supposi- 

 tion the variation in the angles of extinction could be easily accounted 

 for. The conversion of augite into hornblende would, we might 

 naturally expect, have been more complete in some crystals than 

 in others. 



Volcanic ash. 



No. 8 — 277. Volcanic Ash, from Pugfa valley, Ladakh ; collected by 

 R. D. Oldham, F. G. S. 



This specimen is dark green in colour and has a specific gravity 

 of 2*915. Judging from the hand-specimen, the rock either possessed 

 an original laminated structure or a pseudo-lamination has been 

 superinduced by pressure. 



The microscopical examination of this rock does not enable me 

 to speak decidedly regarding its origin. It was probably a very 

 fine-grained ash, but, if so, aqueous agents acting on it after its de- 

 position have removed all evidence of its clastic origin. The rock 

 now consists of a very fine-grained mixture of chlorite and micro- 

 granular epidote (a variety inclining towards zoisite) dotted with 

 magnetite and an opaque substance, white in reflected light, for 

 which there does not seem to be any definite mineral name. It is 

 a product of decomposition and looks like a cross between leucoxene 

 and zoisite. The slice is much permeated by calcite and contains 

 remains of felspars, some of which are triclinic. The rock is prob- 

 ably a highly altered ash. 



No. 8—272. Volcanic Ash, from the Puga valley, Ladakh ; collected by 

 R. D. Oldham, F.G.S.; Sp. G. 2-873. 



This is a very similar rock to the last. It consists of highly 

 altered felspar crystals, or fragments of crystals, scattered about in 

 a groundmass composed of epidote, chlorite, calcite, ferric oxide 

 and the white opaque mineral mentioned in the description of the 



( *3 ) 



