SILURIAN SYSTEM, ij 
This band probably includes also Mr. Griesbach's "earthy, grey 
crinoid limestone." 
It passes up into a series of hard, light grey, siliceous limestones, 
which gradually become less and less calcareous, and pass through cal- 
careous quartzite into the reddish and brown quartzites which form the 
lowest beds of the " Muth quartzite." 
These siliceous limestones contain a few fossils, which, owing to the 
hardness and homogeneity of the rock, can be seen only on the wea- 
thered surfaces ; they include — ■ 
Favosites sp. 
Bellerophon sp. 
and badly preserved casts of cephalopods. In the Parahio valley, near 
Gyetzan (Gaichund), the same beds contain also numerous casts of 
„ . ^ J iJ) Pentamerusoblongus^Sow. The rock is unfor- 
Pentamerus bed. i i i i . 
tunately so hard that fossils cannot be extracted, 
and the identification of Pentamerus oblongus is therefore not abso- 
lutely certain, but the specimens seen on the weathered surface corre- 
spond so closely with that species that they may be referred to it with 
a very great degree of probability. 
It is evident, therefore, that the whole series included between the 
Age of limestone red quartzite below and the white (Muth) quart- 
series, zite above is of silurian age, and includes both 
upper and lower silurian beds. The lowest subdivisions (i to 3) prob- 
ably include the Caradoc and possibly lower stages, while the coral 
limestone may perhaps be referred to the Llandovery or Wenlock 
These correlations, however, are only tentati\ e, and until the collections 
have been worked out in detail, it will be impossible to recognise defi- 
nite horizons with any degree of certainty ; nor, indeed, has such detailed 
work been aimed at in the present memoir, which does not pretend to 
do more than give a somewhat general account of all the stratified rocks 
of Spiti, leaving the determination of the smaller subdivisions for future 
opportunities of detailed study. 
The two lower subdivisions of Stoliczka's "upper silurian" or 
( 27 ) 
