Page 232 - Lokmanya Tilak Samagra (khand 2)

THE GLACIAL PERIOD 19
co-extensive, but, still, in a r<>ugh sense we may take these two
periods as coinciding with each other. It is impossible within
the limits of a short chapter to- give even a summary of the evi-
dence proving the existence of one or more Glacjal epochs in the
Pleistocene period. We may, however, briefly indicate its nature
and see what the geologists and the physicists have to say as·
regards the causes that brought about such extensive changes
of climate in the Quaternary era. The existence of the Glacial
period is no longer a matter of doubt though scientific men
are not agreed as to the causes which produced it. Ice-sheets
have not totally disappeared from the surface of the earth and
we can still watch the action of ice as glaciers in the valleys of
the Alps or in the lands near the Pole, like Greenland which is
still covered with a sheet of ice so thick as to- make it unfit for
the growth of plants or the habitation of animals. Studying
the effects of glacial action in these places geologists have dis-
covered abundant traces of similar action of ice in former times
over the whole of Northern Europe and America. Rounded
and scratched stones, till or boulder-clay, and the rounded appe~r­
ance ofrocks and mountains clearly point out that at one period
in the history of our globe northern parts of Europe and America
must have been covered for a long time with a sheet of ice several
hundreds of feet in thickness. The ice which thus invaded the
northern portion of America and Europe did not all radiate
from the Pole. The evidence of the direction of the striaJ, or
scratches engraved on rocks by ice, undoubtedly proves that
the ice-caps spread out from all elevated places or mountains
in different directions. These ice-sheets of enormous thickness
covered the whole of Scandinavia, filled up the North Sea; in-
invaded Britain down to the Thames valley, greater portion of
Germany and Russia as far south as Moscow and armost as far
east as the Urals. It is calculated that at least a million of square
miles in Europe and more in North America were covered by
the debris of rocks ground down by these glaciers and ice-caps,
and it is from this debris that geologists now infer the existence
of an Ice Age in early times. The examination of this debris
shows that there are at least two series of boulder clay indicat-
ing two periods of glaciation. The debris of the second period
has disturbed the first layer in many places, but enoush remains
to show that there were two dis~et beds of boulder clay and