HAYDEN: GEOLOGY OF SPITI. 
from a soft, argillaceous rock to a hard, siliceous variety with 
much mica. They are very finely laminated and much crushed, 
and the direction of foliation being usually oblique to the bedding, 
the rock frequently resembles a needle shale. The slates are inter- 
bedded with great regularity with grey, yellow or whitish quartzites, 
which are almost invariably capped by a narrow band of either cal- 
careous quartzite or dolomitic limestone only a 
Dolomite. r^, ,. 
few inches in thickness. The limestone, which 
is grey on fresh fracture, weathers to a pinkish or brownish red, and 
is again overlain by slates, which are at first argillaceous but gradually 
become more and more siliceous, till they pass up again into quart- 
zites ; this alternation continues with great regularity for many 
hundred feet. Towards the top of the series the argillaceous beds give 
place to light-coloured siliceous slates and thin-bedded, flaggy quart- 
zites with bands of red and pink dolomite, which latter gradually in- 
creases in frequency and thickness, till it becomes the predominant rock. 
These beds constitute the oldest fossiliferous series hitherto found 
in Spiti. The fossils, which consist chiefly of Lingulella and trilobites, 
are most numerous in the argillaceous beds, but the narrow bands of 
limestone, and, in places, the flaggy quartzites, are also fossiliferous. 
■ The most complete section is seen in the valley of the Parahio, 
where the following sequence of rocks forms the steep hills on the left 
bank of the river, above Maopo E. G.': — 
19. Conglomerate. 
18. Quartzite and siliceous shale . . . about 50 feet. 
17. Grey dolomite, weathering brownish-red . „ 20 „ 
16. Flaggy sandstone, quartzite and siliceous 
slate . . . . . . . „ 40 „ 
15. Grey dolomite, weathering brownish-red . „ 30 „ 
14. Siliceous slates, with grey quartzite bands 
:\nd thin beds of pink dolomite (slates 
chiefly grey and green, but weather pink) . „ 250 „ 
13. Dark siliceous slates, with a few fragmentary 
trilobites „ 10 ,, 
( 14 ) 
Carried over . 400 feet. 
* E. G. = Encamping ground. 
