1919.] History of the Drainage of Northern India. 91 
(2) If the rate of elevation was too rapid for the erosive 
wer of the river to keep pace with it, the latter 
might be elbowed off to the west. 
(3) If the elevation was very sudden and the sea were 
accessible in another direction, the course of the 
river might be altogether reversed. 
Whether the first of these results could have been noticed 
during the early stages of the elevation of the Himalayas or 
even in the Miocene is matter for conjecture, but in any case 
one cannot conceive it operating for long or there would still 
be a great north-westerly flowing river 
he writer is of opinion that the third of these results did 
not happen until after the deposition of the boulder beds in 
the Pleistocene, for, not otherwise than by the train of cireum- 
stances initiated by the second of the three alternatives, can the 
writer account for the formation of the boulder conglomerates. 
The reversal of the drainage concluded the Siwalik epoch 
and inaugurated modern conditions. 
It is essential for the validity of the whole theory that it 
should account not only for the existence of the boulder con- 
glomerates, but also for the special features and distribution 
of the whole series of Siwalik deposits which preceded them 
I, therefore, propose to suggest how the distribution of the 
Siwalik boulder conglomerates may be explained on the hypo- 
thesis in question, and how the whole fluviatile series falls into 
its proper place in the continuons working of the same evolu- 
tionary scheme. 
Before doing this it will be as well to give as brief a 
summary as possible of what we know about.the character 
and distribution of the different members of the series. 
In i 
ing ous ferruginous concretionary masses, of the Bugti 
hills of Baluchistan, also largely lacustrine in origin. a 
similar age are possibly the basal beds of the Dagshai series 
consisting of ferruginous and gypsiferous clays somewhat con- 
cretionary in character. 
The deposits of the Murree- beds, consisting of fine- 
