20 
HAYDEN : GEOLOGY OF SPITI. 
Chapter III. 
SILURIAN SYSTEM. 
Throughout Splti the cambrian beds are overlain by a great 
., . system of shallow-water deposits, broadly con- 
Lower Silurian con* , 
glomerate and quart* sisting of conglomerates at the base, followed 
by grits, and passing up gradually into a thick 
mass of gritty quartzite, with occasional thin bands of shale. 
The age of these rocks has hitherto been regarded as upper 
Silurian. By Stoliczka it was included in his Muth series, of which 
it formed the lowest member; that series he regarded as of "upper 
Silurian " age, but it has already been stated that he most probably 
included the cambrian in his silurian system, and his "upper Silurian" 
would therefore include the whole silurian system of the present 
memoir. 
By Mr. Griesbach the quartzite was regarded as of upper silurian 
age and identified by him with a similar formation found in Kumaon 
and Garhwil. 
In Spiti, internal evidence of the age of the series is entirely 
wanting, for no fossils have been found in it anywhere, but it overlies — 
though unconformably — upper cambrian beds, and underlies a series 
of quartzite, shale and limestone, the lowest beds of which are 
almost certainly not younger than Caradoc. 
The lower silurian system of Spiti has been described by Mr. 
Griesbach as consisting of "thin-bedded, coral limestone of dark grey 
colour, with occasional intercalations of siliceous and shaly beds of 
greenish and pink colour. Near its junction with the red quartz 
shales, beds of dark (fossiliferous) coral limestone alternate with the 
red shales, which are often replaced by greenish-grey beds of other- 
wise similar lithological character."^ The thickness of this series he 
states to be about 300 feet. 
Memoirs, G. S. I., vol. XXII 1, p. Ji». 
( 30 ) 
