Vol. XI, Nos. 5 & 6.] The Geological History of 8.India. 145 
[N.8.] 
These rocks occur in extensive beds or bands in both the 
steep angles there is little doubt that they were once practi- 
capping of these rocks which is still comparatively horizontal 
with moderate undulations and which is still from 300 to 500 feet 
inthickness. They are composed mainly of alternating bands 
bourhood of shore lines. On the other hand, bands of it are 
found to alternate sharply with undoubtedly igneous material 
i the shape of basic flows and sills. On account of these 
difficulties some American geologists consider that the 
corresponding rocks in the Lake Superior region were formed 
in tranquil water mainly as chemical precipitates, and that the 
associated lava flows were sub-aqueous flows. This interesting 
and ingenious hypothesis would tend to render a considerable 
Proportion of the Dharwar flows sub-aquaeous, owing to the 
numerous layers of the banded ferruginous rocks and to the 
absence of conglomerates and coarse sedimentary material in 
origin it is extremely difficult to find a arama ean explana- 
it o a 
Chamnockite series. Whatever the origin of these rocks, there 
w be little doubt that their banded character is largely 
‘econdary. As to their sedimentary or aqueous character, I do 
hot think it can be regarded as definitely proved, although the 
seat consensus of opinion is in favour of such a view. _ 
ass to the quartzites, some of which are 
can as the metamorphosed representatives of sedimentary 
ty Soe ere is a great variety of types and they appear 
quart . rent ages. Many of the beds originally mapped as 
slic; fe have proved on close examination to be altered and 
ed quartz-porphyries, some of which retain enough of the 
