. Animal studies. THE ANIMALS OF THE PAST 423 Even then its hard parts will probably find their way to the bottom. At the bottom the remains will soon be covered by the always dropping sediment. They are on the way to become fossils. Some land animals also might, after death, get carried by a river to the lake or ocean, and find their way to the bottom, where they, too, will become fossils. Or they may die on the banks of the lake or ocean and their bodies may get bnried in the soft mnd of the shores. Or, again, they are often trodden in the mire abont salt springs or submerged in quicksands.
. Animal studies. THE ANIMALS OF THE PAST 423 Even then its hard parts will probably find their way to the bottom. At the bottom the remains will soon be covered by the always dropping sediment. They are on the way to become fossils. Some land animals also might, after death, get carried by a river to the lake or ocean, and find their way to the bottom, where they, too, will become fossils. Or they may die on the banks of the lake or ocean and their bodies may get bnried in the soft mnd of the shores. Or, again, they are often trodden in the mire abont salt springs or submerged in quicksands. It is ob- vious that aquatic animals are far more likely to be pre- served as fossils than land animals. This inference is strikingly proved by fossil remains. Of all the thousands and thousands of kinds of extinct insects, mostly land animals, comparatively few specimens are known as fos- sils. On the other hand, the shell-bearing mollusks and crustaceans are repre- sented in almost all rock deposits which contain any kind of fossil remains. It is obvious that any por- tion Of the earth's Surface Fig. 244.—A fossil brachiopod {Spirifer covered by stratified rocks ITZZl^T^' ^ meaSUreS' must have been at some time under water, the bottom of a lake or ocean. If now this portion shows a series of layers or strata of different kinds of sedimentary rocks, it is evident that it must have been under water several times, or at least under different con- ditions. It is also evident that fossils found in this portion of the earth will contain remains of only those animals which were living at the various times this portion of the earth was under water. Of the animals which lived on it when it was land, there will be no trace, except, possibly, a few land or fresh-water forms which might be swept into the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not p
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