CHAr Tek, Vit 
PAST AND PRESENT 
Tue dependence of animals upon plants for the food 
by means of which they continue to inhabit the earth, 
which was pointed out on a previous page (75), shows 
that the plant world is older than the animal world; 
but the immense age of both can be appreciated only 
by a study of stratigraphical geology. The tens of 
thousands of feet of sedimentary rocks, laid down in 
slow succession on the floors of ancient seas and 
lakes, and still reposing layer upon layer, and no less 
the great gaps in the series produced when, raised 
into the air, deposition ceased, and thousands of feet 
of rock were slowly worn away and washed down 
again into the sea by the action of frost and wind and 
water, point to periods incalculably remote as 
measured by the standards which we apply to human 
history. A few thousands of years measures the 
span which separates us from the Neolithic Period; 
but to the geologist a million years is but a con- 
venient unit for expressing, so far as any expression 
by our time-standards is possible, the huge periods 
with which he has to deal. And even when we get 
back as far as the oldest fossils will take us, we 
are still a long way from having reached the epoch 
when life on the earth originated. As we work back- 
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