LADAKH, NORTH-WESTERN HIMALAYA. 321 



The diallage is very typically developed. It usually polarizes 

 brilliantly in colours of Newton's first order. Here and there it has 

 Suffered alteration to hornblende and in other places into zoisite. 



The felspar, judging from the angle of extinction from the 

 twinning plane of albite twins, is labradorite. The maximum 

 extinction in five suitable cases was 33 £°. It has suffered more or 

 less conversion into zoisite* the change being partial in some cases 

 but complete in others. 



Afo. Q4 — 212. Gabhro, from Peak D. 24. Ladakh ; collected by R. Lydek- 

 ker, F.R.S., F.G.S.; Sp. G. 3-195. 



This rock is composed of olivine and diallage with some picotite, 

 the first mentioned mineral predominating. 



The olivine is fairly fresh and polarizes brilliantly in the blue, red, 

 and yellow of Newton's second order. It is traversed by some 

 aqueous canals but serpentinisation has hardly commenced. 



The diallage, on the other hand, is extremely dull between crossed 

 Nicols and polarizes feebly in shades of grey. 



The rock has evidently sustained considerable pressure. The 

 olivine is much cracked, and here and there puts on a micro- 

 tessellated structure imitative of the tessellated quartz of the Hima- 

 layan granites. Both the olivine and the diallage exhibit strain 

 shadows. Some of the latter also show an interrupted foliation 

 distinct from the fine cleavage. 



PORPHYRITIC DlORITE. 



Collected by R. D. Oldham, A.R.S.xM., F.G.S. 



No. 8 — 27 g. Locality, 2 miles North-East of Isul Tak, North of Chang La, 



Ladakh. 

 No. 8—280. Locality, junction of the Chang and Inchine valleys, Ladakh. 

 No. 8 — 281. Locality, junction of the Chang and Inchine valleys, Ladakh. 



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