LADAKH, NORTH-WESTERN HIMALAYA. 327 



titaniferous-iron in the finely comminuted ash, and in the inclu- 

 sions of the base in the augites. Opaque spots and patches of 

 leucoxene were thus formed in the groundmass, in the pseudo 

 tongues, and in the inclusions. Aqueous infiltration still further 

 masked the clastic character of the rock by converting what remained 

 of the finely comminuted ash into a chloride-serpentine, fine canals 

 of which not only meander about in the groundmass, but penetrate 

 the augites from side to side. 



The augites are nearly all distinctly fragments, though in one case 

 an idiomorphic crystal remains intact. There are also fragments 

 of felspars. They are much altered and contain patches of chloritic 

 serpentinous material and of calcite, or magnesite, and magnetite. 

 The latter is also common in the groundmass. 



The rock under description affords a good object lesson of how 

 aqueous agents, acting on finely comminuted ash, may obliterate 

 evidence of its clastic origin. Where the contact action of igneous 

 intrusive rocks follow the action of aqueous agents still greater 

 difficulties may arise. A really good suite of specimens is sometimes 

 indispensable to enable a petrologist to say positively whether a 

 rock is a highly metamorphosed ash or a highly altered lava. 



No. Q4 — 218. Volcanic Ash y from Wangat, Ladakh j collected by 

 R. Lydekker, F.R.S.; Sp. G. 2-849, The rock occurs with 

 tertiary strata. 



This ash has already been described by me in the Records, 

 Geol. Surv. Ind., Vol. XIX, p. 118 (1886). It is a dark-grey frag- 

 mental rock with a slight greenish tinge. 



Under the microscope the rock is seen to be made up of sub- 

 angular and splintery fragments which vary much in size. Some of 

 them are fragments of acid volcanic rocks such as felsite, rhyolitic 

 lava, and porphyry. There are also pieces of quartz, felspar, crys- 

 talline limestone, and grains of magnetite and titaniferous iron. 

 It is the two last that give the rock its high specific gravity. If we 

 except the iron, which appears to be an original constituent and 



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