Читать книгу Peter Parley's Wonders of the Earth, Sea, and Sky онлайн

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If these layers were perfectly horizontal, laid one over another like the coats of an onion, we should have to dig through one before we could get to the second, and our knowledge of what the globe consists, would be much more limited than it is; for the greatest depth to which men have descended in the deepest mines, is not much greater than the thickness of one of the strata.

But, instead of this, the surface is broken up by some force from beneath elevating portions, so as to form mountains and hills; and in consequence of this the edges of the strata appear on the surface one after another; just as you would see the edges of a row of bricks that had been set up on their ends, and then the last one thrown down so as to push down all the others.

This is the way in which the strata are placed in the neighbourhood of Weymouth.

The chief reason why I wished you to understand this is, that you may see how it is known that one stratum is older than another. It is evident that the substance marked a, in the section, which is limestone, must have been deposited before b, while b must certainly be older than c.