ntic glaciers. Much ice grinds
much mud on those snow-capped summits. The rivers that flowed from the
Roof of the World carried down vast sheets of alluvium, which formed
fans at their mouths, like the cones still deposited on a far smaller
scale in the Lake of Geneva by little lateral torrents. Gradually the
silt thus brought down accumulated on either side, till the rivers ran
together into two great systems--one westward--the Indus, with its four
great tributaries, Jhelum, Chenab, Ravee, Sutlej; one eastward, the
Ganges, reinforced lower down by the sister streams of the Jumna and
the Brahmapootra. The colossal accumulation of silt thus produced
filled up at last all the great arm of the sea between the two mountain
chains, and joined the Deccan by slow degrees to the continent of Asia.
It is still engaged in filling up the Bay of Bengal on one side by the
detritus of the Ganges, and the Arabian Sea on the other by the
sand-banks of the Indus.

In the same way, no doubt, the silt of the Thames, the Humber, the
Rhine, and the Meuse tend slowly (bar accidents) to fill up the North
Sea, and anticipate Sir Edward Watkin by throwing a land bridge across
the English Channel. If ever that should happen, then history will have
repeated itself, for it is just so that the Deccan was joined to the
mainland of Asia.

One question more. Whence comes the mud? The answer is, Mainly from the
detritus of the mountains. There it has two origins. Part of it is
glacial, part of it is leaf-mould. In order to feel we have really got
to the very bottom of the mud problem--and we are nothing if not
thorough--we must examine in brief these two separate origins.

The glacier mud is of a very simple nature. It is disintegrated rock,
worn small by the enormous millstone of ice that rolls slowly over the
bed, and deposited in part as 'terminal moraine' near the summer
melting-point. It is the quantity of mud thus produced, and borne down
by mountain torrents, that makes the alluvial plains collect so quickly
at their base. The mud flats of the world are in large part the wear
and tear of the eternal hills under the planing action of the eternal
glaciers.

But let us be just to our friends. A large part is also due to the
industrious earth-worm, whose place in nature Darwin first taught us to
estimate at its proper worth. For there is much detritus and much
first-rate soil even on hills not covered by glaciers. Some of this
takes its origin,