328 MCMAHON : PETROLOGICAL NOTES ON SOME PERIDOTITES, ETC., 



not a secondary product of infiltration, none of the fragments were 

 derived from basic lavas or ultra-basic igneous rocks. I have not 

 detected any ferro-magnesian mineral in the slices cut from this 

 specimen. Besides the above-named rocks the thin slices also contain 

 grains of calcite and fragments of quartz and felspar. 



The fragments of which the rock is made up are the reverse of 

 fresh, but the alteration set up in them seems to have taken place 

 before the formation of the ash. The thin slices are not stained or 

 streaked by any visible aqueous agents. 



The ash reminds me of the ash-like fragmental rock which 

 occurs in the Gupis-Yasin section of the Yasin valley described in 

 my paper on the Geology of Gilgit (Quart. Journ. Geol. Soc, Vol. 56, 

 pp. 357, 358). They must both have been derived from very similar 

 rocks. 



No. Q4 — 224. Fine-grained Ash, from Wangat, Ladakh ; collected by 

 R. Lydekker, F.R.S.; Sp. G. 27^, Said to be of eocene age. 



This is a greenish grey and very fine-grained fragmental rock. 



It is made up of subangular fragments very closely packed together. 



They are all small, but vary much in relative size. None of them 



are water-worn and there is no parallelism, or lamination, in their 



arrangement, the longer axes of the fragments being orientated in 



all directions. 



Some of the fragments can be definitely recognised as lavas, 



but the majority cannot be identified as such. They consist of 



angular, subangular, or splintery pieces of quartz, triclinic felspar, 



crystalline limestone, granite, and schist. Some of the quartz 



grains contain numerous liquid cavities with movable bubbles and 



were evidently derived from a granite. Some fragments apparently 



came from porphyries or rhyolitic rocks. 



Tnc slices contain dots and patches of red or dark brown ferrite, 



but no ferro-magnesian mineral, or fragment of a basic igneous rock. 



Except in its finer gfein, and in the absence of magnetite, it very 



much resembles the last«mentioned specimen. The fragments are 



( *6 ) 



