tween the mountains of the eastern and western portion of America were formed from the sediment washed down from these mountains and deposited in the sea which lay between.
The crust of the earth is still rising and sinking, the land gaining on the water, but as this is usually such a slow movement, it can only be traced through a period of many years.
"The notion that the ground is naturally steadfast is an error. The idea of terra firma belongs with the ancient belief that the earth was the center of the universe. It is, indeed, by their mobility that the continents survive the increasing assaults of the ocean waves, and the continuous down-wearing which the rivers and glaciers bring about."
Nearly the whole of Sweden and Norway, for instance, has been rising for thousands of years. This is proved by the fact that old sea-beaches full of shells of species now living in neighboring seas, are found from fifty to seventy miles inland, and several hundred feet above the present sea-level on both sides of the Scandinavian peninsula.[1] Such sea-beaches are found high above the present water level in Chile and Patagonia, and the chalk cliffs of England were formed under the waves of the ocean. Le Conte says that one of the most evident proofs of crustal movements in ancient geologic times is the great thickness of shallow water sediments (sandstones, shales and limestones) over the greater portions of all of the continents, which represent areas of slow subsidence; and the great breaks or unconformities between the series of strata, which represent areas of uplift and atmospheric erosion.
Although sand and gravel are distributed over the bottom of the ocean near the land, dredging expeditions reaching down their metal cylinders for samples of the sea-floor at greater depths in various sections of the globe, have discovered that it is of a different composition, one-third of its area being covered with red clay.
- ↑ De Greer, Bulletin of the Geological Society of America, vol. III, 1892.
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