CHAPTER 13.
CHRONOLOGICAL RELATIONS OF THE GLACIAL PERIOD AND THE EARLIEST SIGNS OF MAN'S APPEARANCE IN EUROPE.
Chronological Relations of the Close of the Glacial Period and the earliest geological Signs of the Appearance of Man. Effects of Glaciers and Icebergs in polishing and scoring Rocks. Scandinavia once encrusted with Ice like Greenland. Outward Movement of Continental Ice in Greenland. Mild Climate of Greenland in the Miocene Period. Erratics of Recent Period in Sweden. Glacial State of Sweden in the Pleistocene Period. Scotland formerly encrusted with Ice. Its subsequent Submergence and Re-elevation. Latest Changes produced by Glaciers in Scotland. Remains of the Mammoth and Reindeer in Scotch Boulder Clay. Parallel Roads of Glen Roy formed in Glacier Lakes. Comparatively modern Date of these Shelves.
The chronological relations of the human and glacial periods were
frequently alluded to in the last chapter, and the sections
obtained near Bedford, and at Hoxne, in Suffolk, and a general view
of the Norfolk cliffs, have taught us that the earliest signs of
Man's appearance in the British isles, hitherto detected, are of
post-glacial date. We may now therefore inquire whether the
peopling of Europe by the human race and by the mammoth and other
mammalia now extinct, was brought about during the concluding
phases of the glacial epoch.
Although it may be impossible in the present state of our knowledge
to come to a positive conclusion on this head, I know of no inquiry
better fitted to clear up our views respecting the geological state
of the northern hemisphere at the time when the fabricators of the
flint implements of the Amiens type flourished. I shall therefore
now proceed to consider the chronological relations of that ancient
people with the final retreat of the glaciers from the mountains of
Scandinavia, Scotland, Wales, and Switzerland.
SUPERFICIAL MARKINGS AND DEPOSITS LEFT BY GLACIERS AND ICEBERGS.
In order fully to discuss this question, I must begin by referring
to some of the newest theoretical opinions entertained on the
glacial question. When treating of this subject in the "Principles
of Geology," chapter 15, and in the "Manual (or Elements) of
Geology," chapter 11, I have stated that the whole mass of the ice
in a glacier is in constant motion, and that the blocks of stone
detached from boundary precipices, and the mud and sand swept down
by avalanches of snow, or by rain from the surrounding heights, are
lodged upon the surface and slowly borne along in lengthened
mounds, called in Switzerland moraines. These accumulations of
rocky fragments and detrital matter are left at the termination of
the glacier, where it melts in a confused heap called the "terminal
moraine," which is unstratified, because all the blocks, large and
small, as well as the sand and the finest mud, are carried to equal
distances and quietly deposited in a confused mass without being
subjected to the sorting power of running water, which would convey
the finer materials farther than the coarser ones, and would
produce, as the strength of the current varied from time to time in
the same place, a stratified arrangement.
In those regions where glaciers reach the sea, and where large
masses of ice break off and float away, moraines, such as I have
just alluded to, may be transported to indefinite distances, and
may be deposited on the bottom of the sea wherever the ice happens
to melt. If the liquefaction take place when the berg has run
aground and is stationary, and if there be no current, the heap of
angular and rounded stones, mixed with sand and mud, may fall to
the bottom in an unstratified form called "till" in Scotland, and
which has been shown in the last chapter to abound in the Norfolk
cliffs; but should the action of a current intervene at certain
points or at certain seasons, then the materials will be sorted as
they fall, and arranged in layers according to their relative
weight and size. Hence there will be passages from till to
stratified clay, gravel, and sand.