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Updated: May 18, 2025
In many parts if you could dig straight downwards through the earth for thousands of feet, you would come to layer after layer of these stratified rocks, one kind below another, some layers thick, some layers thin, here a stratum of gravel, there a stratum of sandstone, here a stratum of coal, there a stratum of clay. But how, when, where, did the building up of all these rock-layers take place?
They are rarely, if ever, seen in unstratified rocks; but many layers of stratified rocks abound in these remains. Whole skeletons as well as single bones, whole tree-trunks as well as single leaves, are found thus embedded in rock-layers, where in ages past the animal or plant died and found a grave.
For there is a certain sort of order followed in the arrangement of rock-layers all over the earth, and it is well known that some rocks are never found below some other rocks, that certain particular kinds are never placed above certain other kinds.
Although in the first instance the succession of fossils was understood by means of the succession of rock-layers, yet in the second place the arrangement of rock-layers is made more clear by the means of these very fossils. A geologist, looking at the rocks in America, can say which there were first-formed, which second-formed, which third-formed.
These buried forests lay through the ages following, slowly hardening into the black and shining coal, so useful now to man. The coal is found thus in thin or thick seams, with other rock-layers between, telling each its history of centuries long past.
Below the sea, as the rock-layers were being formed, bit by bit, of earth dropping from the ocean to the ocean's floor, sea-creatures lived out their lives and died by thousands, to sink to that same floor. Millions passed away, dissolving and leaving no trace behind; but thousands were preserved shells often, animals sometimes. Nor was this all.
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