88 Journal of the Asiatic Society of Bengal. [N.S., XV, 
well sae ilk everywhere in the Himalayas as in Kangra and 
Jamm 
The best testimony to the inefficacy of a river with a 
regular gradient to deposit the Siwalik boulder beds exists in 
the absolute failure of thé modern Ganges and Brahmaputra to 
produce anything of the kind, and also of the Irrawaddy during 
the Miocene and Pliocene to accumulate any pebble beds in its 
deposits. Moreover the almost entire absence of pebbles in the 
lower portions of the freshwater series of India and their scar- 
oey except in the uppermost beds of the — is not explicable 
except by invoking some factor which was not in operation 
previously to the epoch of the boulder zone. 
3) There is, however, one well-known cause which is res- 
ponsible for the formation of pebble beds where none had 
previously existed. If any portion of the channel of a river is 
elevated, the depression produced behind this fold becomes a 
basin of deposition; the deposit will continue, other things 
being equal, until the basin is filled up and the regular down- 
ward gradient of the river is restored. If this basin has been 
produced near a hilly country, where large boulders are often 
being detached, a series of conglomerates will be deposited. 
Vredenburg ! has pointed out how a slight earth movement in 
the Peninsula during the Pleistocene produced basins in the 
upper courses of the Narbada and Godavari as a result of which 
over 500 feet of sediment were laid down over a considerable 
area. In this deposit are many pebbles, but, on account of the 
remoteness of the hills, no boulder beds were formed. When 
these sediments had filled up their basins, the rivers recovered 
their former gradients sat ceased to deposit, while at a still 
later date they cut into the gravels which had been laid down 
in the Pleistocene. 
This is almost precisely what seems to have happened, only 
on a much larger scale and pc coon by intense folding, in 
the Siwaliks. Sedimentation appears to have taken place in a 
broad river valley, into which ne entered from the 
affluents would accumulate. It may be that during the lower 
Pleistocene, on account of excessive rainfall, debris eu 
these tributaries brought down was largely in reased in 
tity as La Touche has suggested. It is also potable thee ‘is 
fragments would increase in size and in amount the nearer one 
1 E. iar pom Pleistocene movement as indicated by irregularities 
of gradient of the Narbada and other rivers in the Indian Peninsula. Rec. 
Geol. Surv., Tndlse. XXXIII, pp. 33-45 (1906). 
