vil THE ANTIQUITY AND ORIGIN OF MAN 417 
But this state of belief in opposition to facts could not 
long continue. In 1859 a few of our most eminent geologists 
examined for themselves into the alleged occurrence of flint 
implements in the gravels of the north of France, which had 
been made public fourteen years before, and found them 
strictly correct. The caverns of Devonshire were about the 
same time carefully examined by equally eminent observers, 
and were found fully to bear out the statements of those 
who had published their results eighteen years before. Flint 
implements began to be found in all suitable localities in 
the south of England, when carefully searched for, often in 
gravels of equal antiquity with those of France. Caverns 
giving evidence of human occupation at various remote 
periods were explored in Belgium and the south of France— 
lake-dwellings were examined in Switzerland—refuse-heaps in 
Denmark—and thus a whole series of remains have been 
discovered carrying back the history of mankind from the 
earliest historic periods to a long distant past. 
The antiquity of the races thus discovered cannot be 
measured in years; but it may be approximately determined 
by the successively earlier and earlier stages of civilisation 
through which we can trace them, and by the changes in 
physical geography and of animal and vegetable life that 
have since occurred. As we go back metals soon disappear, 
and we find only tools and weapons of stone and of bone. 
The stone weapons get ruder and ruder; pottery, and then 
the bone implements, cease to occur; and in the earliest 
stage we find only chipped flints of rude design, though 
still of unmistakably human workmanship. In like manner 
domestic animals disappear as we go backward; and though 
the dog seems to have been the earliest, it is doubtful 
whether the makers of the ruder flint implements of the 
gravels possessed even this. Still more important as a 
measure of time are the changes in the distribution of 
animals, indicating changes of climate, which have occurred 
during the human period. At a comparatively recent epoch 
in the record of prehistoric times we find that the Baltic 
was far salter than it is now and produced abundance of 
oysters, and that Denmark was covered with pine forests 
inhabited by Capercailzies, such as now only occur farther 
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