90 REPORT—185/7. 
On Erosion of Rivers in India. 
By Hermann and Rosert ScHLAGINTWEIT. 
Amongst the phenomena which characterize the course of large tropical rivers, and 
which, although not entirely wanting in European rivers, are still but very imperfectly 
developed in them, are the considerable alterations in their amount of water, recurring 
eriodically at various seasons of the year, the amount of their suspended matter, atid 
especially the astonishing vastness of their erosions. The erosion of the rivers consists 
in their constantly deepening their beds, and thus slowly, but constantly receding 
from the general surface. 
It is indeed the erosion that is most highly and generally developed in Indian 
rivers, both in their lower course in the plains, and especially in their middle and 
upper course in the mountains, in the Himalaya and in Tibet. When correctly 
recognized and determined, it is moreover interesting, because it furnishes important 
data for the explanation of many geographical, geological and physical conditions. 
But before referring to some of the numerous phenomena which stand partly in 
intimate connexion with the erosion of rivers, and are partly an immediate conse- 
quence thereof, we venture to illustrate the vastness and universal extension of the 
erosion of Indian rivers by a few examples and numbers. 
The erosion is greatest in the upper course of the river, in the mountains. But 
even in the plains it is generally recognisable, and even here it not unfrequently 
attains a magnitude of 80 to 120 feet. : 
But in the Himalaya and Tibet the average magnitude of the erosion of the rivers, 
even the small ones, amounts to 1200—1500 feet, frequently exceeds 2000 feet, 
and in some cases, as in the upper course of the Ganges, the Sutlej and the Indus, 
even attains the extraordinary magnitude of 3000 feet, or, to express ourselves more 
generally, the bed of each of these rivers was originally in the most extreme cases, 
3000 feet higher than at present; and a stratum, partly of solid rock, partly of allu- 
vium of a thickness of 3000 feet, has been Pate. 
These relative magnitudes were so surprising, and the effects of erosion in general 
were so new a subject of investigation, that we had at first much difficulty in find- 
ing those data which might guide us in the definitive determination of the mag- 
iitude of the erosion. A summary of the various topographical forms which served 
us as well-defined starting-points in the determination of the magnitudes, with a short 
discussion of the value of each of these forms, may not be without interest. 
The most essential positive data for the determination of erosion are :— 
Spoon-shaped erosions in the walls of valleys ; detritus, partly different from, partly 
identical with those still occurring in the river (which are often deposited on level 
surfaces) ; and connected lines of conglomerates of sand and freshwater shells along 
the steep walls of the valleys. In the Himalaya and in Tibet these often occurred, 
most distinctly marked, at elevations exceeding the level of the present bed of the 
river by 3000 feet. 
In the most various rivers, and under the most multifarious conditions, some, but 
certainly not all the forms which we have just cited as characteristic of erosiun, were 
always present, so that we were able in almost all places to measure the erosion 
directly, and to determine it niore accurately than the subject would lead one to expect. 
In the plains, as has already been mentioned, the magnitude of the erosion is much 
less, namely 80 to 120 feet, but the form is perfectly different. 
From the Kaveri, Pener, Kistna and Godavery, in the south of India, and from the 
rivers of central India up to the plain of the Ganges, all the rivers have a distinetly 
tiatked bed of erosion, in which two stages are to be distinguished; one for the average 
height of the lower or ordinary height of water; and the other, the rainy river-bed, for 
the maximum height of the water. 
The magnitude of the rainy river-bed is astonishing; in the lower course of the 
Ganges, the Brahmaputra and the Indus, it sometimes amounts to three or four miles, 
whilst the bed for the average-water level is about one mile in breadth. It is remark- 
able that the rainy river-bed increases in relative size the smaller the regular bed of 
the river is. ust 
During nine months of the year the river runs in its regular bed, whilst its rainy” 
bed lies dry, bearing fruitful crops on some riyers, such as the Ganges and Jumna_ 
