to the Ganges. The gravel-beds extend upon the
plains for fully twenty miles south of the Sikkim
mountains, the gravel becoming smaller as the distance
increases, and large blocks of stone not being found
beyond a few miles from the Himalaya itself, even in
the beds of rivers, however large and rapid. Throughout
its breadth this formation is conspicuously cut into
flat-topped terraces, flanking the spurs of the mountains,
at elevations varying from 250 to nearly 1000 feet
above the sea. This deposit contains no fossils; and
its general appearance and mineral constituents are
the only evidence of its origin, which is no doubt due
to a retiring ocean that once washed the base of the
Sikkim Himalaya, received the contents of its rivers,
and, wearing away its bluff spurs, spread a talus
upwards of 1000 feet thick along its shores.
The alluvium of the Gangetic valley was no doubt
deposited in deep water, whilst the coarser matter was
accumulating at the foot of the mountains.
This view has occurred, I believe, to almost every
observer, at whatever part of the base of the Himalaya
he may have studied this deposit. Its position
indicates its recent formation; but it still remains a
subject of the utmost importance to discover the extent
and nature of the ocean to whose agency it is referred.
The alluvium of the Gangetic valley may to a great
degree be the measure of the denudation which the
Himalaya has suffered along its Indian watershed.
I t was, no doubt, during the gradual rise of that chain
from the ocean, that the gravel and alluvium were
deposited; and in the terracing and alternation of
these deposits, there is evidence that there have been
many subsidences and elevations of the coast-line,
during which the gravel has suffered greatly from
denudation.
I never looked at the Sikkim Himalaya from the
plains without comparing its bold spurs enclosing
sinuous river gorges, to the weather-beaten front of a
mountainous coast; and in following any of its great
rivers, the scenery of its deep valleys no less strikingly
resembles that of such narrow arms of the sea (or
fiords) as characterise every mountainous coast, of whatever
geological formation: such as the west coasts of
Scotland and Norway, of South Chili and Fuegia, of
New Zealand and Tasmania. There are too in these
Himalayan valleys terraced pebble-beds, rising in some
cases eighty feet above the rivers, which I believe
could only have been deposited by them when they
debouched into deep water; and both these, and the beds
of the rivers, are strewed with masses of rock. Such
accumulations and transported blocks are seen on the
raised beaches of our narrow Scottish salt water lochs,
exposed by the rising of the land, and they are yet
forming of immense thickness on many coasts by the
joint action of tides and streams.
In every Himalayan valley which I ascended, I met
with ancient moraines at or about 7000 or 8000 feet
elevation, proving, that at one period, the glaciers descended
fully so much below the position they now
occupy : this can only be explained by a change of
climate, or by a depression of the mountain mass equal
to 8000 feet, since the formation of these moraines.