66 
Becords of the Geoloykal Survey of India. 
[vOL. XII. 
Glaciation. 
On the top of Cliandan Namo pass (close to the Ga station, above Chango), 
i obsei'ved a considerable number of rounded i-iver boulders of red quartzite and 
other rocks that do not occur locally. The red quartzite was probably derived 
from the Muth beds in Spiti. Beyond and at a lower level, I occasionally met 
with rounded boulders of trap, doubtless from the palseozoic formation of 
that valley (Memoirs, vol. V, p, 20), whilst 670 feet above the Para river, 1 
observed numerous horizontal beds of river conglomerate. The boulders on the 
top of the Chandan Kamo pass were undoubtedly rounded in the bed of a river 
by the action of the w’ater, and there are no grounds for supposing that they w^ere 
ice borne. The only exjilanation that appears reasonable to me is that the bed 
of the Spiti river was formerly as high as the top of the Chandan Name pass, 
which is about 2,400 fcoP above the present bed of the Spiti river. 
Dr. Croll, in chapter XX of his Climate and Time, and Professor Geikie in 
chapter XXV of Juke’s and Geikie’s Manual of Geology (3rd edition, 1872), 
discuss the rate of the erosion of rock surfaces evidenced by the amount of sedi¬ 
ment annually carried down by the river systems ; and the rate of erosion at 
which seven rivers specihed remove one foot of rock from the general surface of 
their basins is said to vary from 6,346 years in the case of the Danube, and 6,000 
years in the case of the. Mississippi, to 929 years in the case of the Po. The rate 
given for the Ganges is one foot in 2,3f>8 years. 
Professor Geikie takes “ the proportion between the extent of the jilains and 
table lands of a country and the area of its valleys to be as nine to one,” and 
assumes “ that the erosion of the surface is nine times greater over the latter than 
over the former area.” If, adopting this principle, we assume that within the 
mountain valleys of the Gangetic ba.sin the erosion is nine times more rapid than 
over the rest of the basin, this would make the rate of erosion over the mountain 
area one foot in 262 j'ears. 
But the agents of denudation are much more powerful within the river basin 
of the Ganges than within that of the Sutlej. The watershed of the Ganges 
embraces a large area of exceptionally heavy rainfall, rising as high as 524 inches 
per annum in the Khasi hills, being “the greatest rainfall in the world,” 
(Huxley’s Physiograjihy, p. 48) ; and within this area the agents of denudation 
must operate with exceptional activity. The rainfall over the watershed of the 
Sutlej, on the other hand, is comparatively light, being probably greatest at 
Simla, where the average for 15 years, from 1862-63 to 1876-77, was 75T inches. 
As you proceed higher up the Sutlej, the fall decreases, and beyond Wangtu 
becomes extremely light. 
1 Measured by ray aneroid barometer, tlio elevation of the S 2 nti river at Leo is 9,550 feet, and 
at the confluence of the Glut river 10,125 feet, the distance between the two jioints, measured 
straight across the map, being 1.3 miles. The top of the pass measured by my barometer is 12,340 
feet. The weather !)eiug fine and cloudless, there could have been little variation from climatic 
cau,ses. 
