32 HAYDEN: GEOLOGY OF THE PROVINCES OF TSANG AND 0, 
with many bands of concretions, eminently suited for the preserva- 
tion of fossils, which, however, only appear in the highest beds, the 
eastern representatives of the Spiti shales ; these contain fragmentary 
ammonites, similar to those collected by Mr. Claude White in the hills 
between Giri and Kampa dzong. Above the Spiti shales on the left 
bank of the Giri river is a contorted series of limestone which 
presumably belongs to the Cretaceous system. Immediately to the 
north of this the valley of the Giri river marks an important line of 
faulting running E.-W., which brings up on the north side of the river. 
Jurassic quartzites and slates overlain by Spiti shales, which continue 
northward almost to the Kampa ridge (see PI. 8, fig. i). The 
above sequence may be tabulated as follows in descending order: 
Limestone (? Neocomian.) 
4. Dark shales with ammonites (Spiti shales.) 
3. „ „ without fossils. 
2. ? ? (hidden by moraines). 
r. Slate, quartzite and conglomerate with RJiynchonella of. quadriplicata 
Ziet. and crinoids. 
(d) Naku La to Kampa dzong. 
Turning now from the eastern to the western side of Chomoyumo, 
we find that a high snow-clad range trending first to the south- 
west then to the west separates;Sikkim from Tibet; this has already 
been referred to as the Lhonak range. Immediately to the west 
of Chomoyumo this range is crossed by the Naku La. To the north 
of the pass the rocks are hidden by talus and moraines, composed 
of granite blocks derived from the central mass of Chomoyumo ; near 
the foot of the slope which is several miles in length, a ridge of slate 
and quartzite stands out prominently above the plain ; the beds of 
this ridge appear to be the westerly continuation of the slates and 
quartzites which form the northern spurs of Chomoyumo. To the 
north they are overlain by somewhat less altered slate with quartzite 
and a narrow band of limestone gradually passing up into upper 
Jurassic rocks and Spiti shales, which extend almost to Kampa dzong. 
( 153 ) 
