1919.] History of the Drainage of Northern India. 87 
ally get broken up into smaller and smaller fragments and 
eventually these and the eee detritus either reach the sea, 
r form material fine enough to eposited on the land by the 
river when in flood, so that in a river with a iagre! ‘asian 
the boulders do not accumulate beyond a certain lim 
For a precisely similar reason to which the mounds a the foot 
of the hills owe their origin, the basal bed of a continental for- 
mation is generally a conglomerate because it represents frag- 
ments that have become detached from a surface that is freshly 
exposed to denudation without being furnished with adequate 
drainage. Consequently a collection of ens ers is formed, 
which may be widespread but is covered up as soon as rivers 
begin to flood their banks and deposit pala fine sedi- 
ment. 
Medlicott’s suggestion,! endorsed by Middlemiss,* that 
these beds were formed by rivers debouching from the hills in 
the same position as they do now, founded on his observation 
that the boulders show signs of be eing more numerous in the 
vicinity of these rivers than elsewhere, is no doubt true so ane 
as it goes. At the same time the boulder conglomerates are ve 
far from being limited to such areas, and though Medlicott s 
b 
to account for the boulder conglomerates reaching such 
lavan rivers. 
Equally true may have been La Touche’s suggestion that 
excessive rainfall and increased erosion are largely responsible 
for the pebble beds that were accumulated in Pleistocene 
ti 
It may well be that the glacial period in India was heralded 
nf one of phenomenal rainfall, and under such conditions an 
reased number of boulders would be brought down from the 
hills and would be carried further afield, but to anyone who 
has seen these Siwalik conglomerates it will, I think, be 
obvious that, with the utmost allowance for increased precipita- 
also seems no reason why the boulder bed should not be as 
oe: aN A herein the Leche and Sse of - southern dees 
of the Himalaya: een the rivers Ganges and Ravi 
—. Surv., Indic, TIT, 2 ( 2 soa) pp- 119, 135. 
2C. iddl 
8 T. D. La Touche, Helios - the great Ice ep in the plains of North- 
ern India. Geol. Mag., Dec. 5, VII (1910), p 
