36 
HAYDEN: GEOLOGY OF SPITI. 
systems, till in the Thanam valley they lie on the red, lower silurian 
quartzite ; as they are traced further eastwards, the upper beds of 
the Silurian re-appear, till at length, near Hango in Kanaur, a few 
patches of the Muth quartzite are found ; these gradually pass into the 
full thickness of that formation, and in the valley of the Lipak river, 
the upper palaeozoic systems occur in the fullest development to which 
they have hitherto been known to attain in the Himalayas. 
Here the Muth quartzite is overlain by a series of limestone 
Carboniferous lime- quartzite over 2,000 feet thick, which is 
stones of Kanaur. turn succeeded by an even greater thickness 
of dark shale and quartzite, passing up near Po, in the Spiti valley, 
into conglomerate and calcareous sandstone, which immediately underlie 
the permian " Productus shales." This great series, the total thick- 
ness of which, including the " Productus shales," cannot be less than 
5,000 feet, represents the carboniferous and permian — and probably 
also devonian — systems of the Himalayas. 
Lithologically, the series falls into two subdivisions, a lower consist- 
ing of quartzite and limestone, and a higher composed of quartzite and 
shale. 
The lower subdivision is found in its fullest development in 
the hills above Lio in Kanaur, where it forms the ridge separating the 
Lipak and Yulang rivers. At the opposite end of Spiti, at the head 
of the Spiti river, it is also largely developed, but the total thickness 
is probably less than in Kanaur ; the beds, however, are crushed 
and faulted, and only a few of the Lipak horizons can be recognised. 
At the point where the upper mountain track to Hango leaves 
the Lipak river, the hills on either side of the stream rise sharply 
up in steep precipices to a height of some 4,000 feet above the 
river ; those on the left bank form one side of the ridge which 
separates the Lipak and Yulang rivers. Near the summit of the 
ridge is the camping-ground of Tangd, between which and the river 
below the rocks afford a section of almost the whole of the silurian 
system, with the Muth quartzite and the overlying limestone and 
quartzite series. Near the middle of the section a bright, reddish* 
( 36 ) 
