142 DYNAMICAL GEOLOGY, 



The animals generally of the ocean are little liable to extermination from 

 changes of climate over the land. ; and hence some marine invertebrate species 

 of the early Tertiary, many of the later, and all of the Quaternary, have 

 continued on until now, while, as regards terrestrial animal life, there were 

 in this interval many successive faunas. 



The loivest species of life are the best rock-maTcers ; namely, Corals, Cri- 

 noids, Rhizopods, Diatoms, Millepores, Bryozoans, Brachiopods, Mollusks ; 

 for the reason that the structures of only the simplest kinds can consist 

 mostly of stone and still perform all their functions. Multiplication of bulk 

 for bulk is more rapid with the minute and simple species than with the 

 higher kinds ; for all animals grow principally by the multiplication of cells; 

 and when single cells or minute groups of them, as in the Khizopods, are 

 independent animals, the increase may still be the same in rate per cubic 

 foot, or even much more rapid, on account of the simplicity of structure. 



While, therefore, we may conclude that we have, in known fossils, a fair 

 though incomplete representation of the marine life of the globe, we know 

 very little of its terrestrial life, — enough to assure us of its general course 

 of progress, but not enough for any estimate of the number of living species 

 over the land ; or for safe deductions as to lines of succession. 



Geology may have within reach of study fossils representing a twentieth 

 of its marine life ; but it has not more than a thousandth of its terres- 

 trial life. 



Some examples of marine accumulation. — (1) Beds of oysters, along with 

 other living species, exist in the shallow seas, as off the coast of North 

 America, but in waters too deep for disturbance by the waves. Sands or earth 

 encroach upon them through the marine currents, but not to the destruction 

 of the species. Afterward, through some geological change, beds of detritus 

 are washed over them, exterminating the oysters and perhaps other species 

 also. This is one case; and in it the fossils are unbroken. (2) In another 

 place, the relics of the life of the coast, the shells, Corals, Crustaceans, etc., 

 live so near the sea level as to be within reach of the waves, and hence they 

 may be dislodged at times of heavy storms, and may become ground into 

 fragments and sand ; or they may be contributed to under- water banks, and 

 some of the shells may be scarcely worn, and therefore good fossils. (3) In 

 another case, the worn fragments, coarse and fine, may be washed up a beach 

 and ground fine or coarse by wave action. (4) Again, the species may live 

 over seashore flats which are so shallow that the triturating waves act gently, 

 and all relics thereby become ground to mud, and not one is left to make a 

 distinguishable fossil. (5) Again, where barriers off a seacoast exclude the 

 salt water with its marine life, not a sea-relic of any kind may be put into 

 the accumulating seashore beds until some change of conditions removes the 

 barrier. 



3. Methods of Fossilization. 



In the simplest kind of fossilization there is merely a burial of the relic 

 in earth or accumulating detritus, where it undergoes no change. Examples 



