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Updated: May 4, 2025
In past geological times it was the site of a vast system of lakes, but the climate has since changed and the water of most of these lakes has evaporated and the sediments of the old lake beds are now desert sands. The ancient lake shores are often represented by conspicuous terraces, each one marking a stage in the height of a dead lake.
Other evidence going to show the extent to which the movements of the earth's crust are affected by the weight of materials are found in the fact that wherever along the shores thick deposits of sediments are accumulated the tendency of the region where they lie is gradually to sink downward, so that strata having an aggregate thickness of ten thousand feet or more may be accumulated in a sea which was always shallow.
The worm is serrated on the one side, each segment having 1 1/2 cusps. The urine pale, faintly acid at first, within the last week became almost neutral. There was considerable vesical irritation for the first week, with abundant mucus in the urine, specific gravity was 1010; there were no albumin nor tube-casts nor uric acid in the urinary sediments. Later there were pus-cells and abundant pus.
Truly, that looks a very simple process! It would be so except for certain difficulties, the very first of which is that of finding how rapidly sediments are deposited; but the main difficulty a difficulty which renders any certain calculations of such a matter out of the question is this, the sea-bottom on which the deposit takes place is continually shifting.
But far the greater part of the plateau is good sound desert, rocky, sandy, or fluffy with loose ashes and dust, dissected in some places into a labyrinth of stream-channel chasms like cracks in a dry clay-bed, or the narrow slit crevasses of glaciers blackened with lava flows, dotted with volcanoes and beautiful buttes, and lined with long continuous escarpments a vast bed of sediments of an ancient sea-bottom, still nearly as level as when first laid down after being heaved into the sky a mile or two high.
But, by rubbing up some chalk with a brush in water and then pouring off the milky fluid, so as to obtain sediments of different degrees of fineness, the granules and the minute rounded bodies may be pretty well separated from one another, and submitted to microscopic examination, either as opaque or as transparent objects.
Between these blocks of sedimentary rocks oozed up through the lines of fracture quantities of fused material, which also sometimes formed mountain chains; and it is possible and even probable that the rocks composing the volcanic ridges are but phases of the same materials that form the sedimentary chains There is, therefore, no a priori reason why the leaching of one group should furnish more ore than the other; but, as a matter of fact, the unfused sediments are much the richer in ore deposits.
If the sediments are marine, we may know also whether they were laid in shoal water near the shore or in deeper water out at sea, and whether during a period of emergence, or during a period of subsidence when the sea transgressed the land. By the same means each formation records the stage in the cycle of erosion of the land mass from which its sediments were derived.
Knowing how slowly sediments accumulate upon the sea floor, we must believe that the successive cycles which the earth has seen stretch back into a past almost inconceivably remote, and measure tens of millions and perhaps even hundreds of millions of years. A complete set of the volumes of the record is to be found in no single region.
We have as yet no data of a precise kind for determining the average rate of accumulation of sediments upon the sea floor, but from what is known of the wearing of the lands, and the amount of volcanic waste which finds its way to the seas, it is probably not less than about a foot in ten thousand years; it is most likely, indeed, much to exceed this amount.
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