India owes much of its fertility to the fact that its soil is
constantly being replenished by alluvium brought down from its high
mountains by its immense rivers. The valleys of the Indus (1800 miles
long), the Ganges (1600 miles long), and the Brahmapootra (1500 miles
long) include an area of 1,125,000 square miles, a part of which, the
Indus-Ganges plain, consists of a great stretch of alluvial soil whose
fertility is as rich as that of any portion of the globe. One hundred
and eighty millions of people live in this plain. So finely pulverised
is its soil that for a distance of almost 2000 miles not even a pebble
can be found in it. And so fertile is it that there are some
agricultural districts in the plain where the population exceeds 900
to the square mile. In that part of the plain which the Ganges waters,
60,000,000 of people find support on the soil by agriculture, at a
density of over 700 persons to the square mile, which is 140 persons
more to the square mile than the density of Belgium, the most thickly
populated country in Europe.