RELATION OE BIOLOGY TO GEOLOGICAL INVESTIGATION. 253 



Because even the hardest and most enduring of the component sub- 

 stances of animalsand plants become entirely decomposed if continuously 

 exposed to the atmosphere after death, it is necessary to their permanent 

 preservation that they should fall under such conditions as exclude the 

 atmosphere. Almost the only way in which this can be accomplished 

 in a natural manner is by their subaqueous intombment in the con 

 stantly accumulating sedimentu which are deposited at the bottom of 

 all bodies of water. In the cases of aquatic animals such intombment 

 of their remains is a necessary result of the nature of their habitat, but 

 the remains of land animals and plants must reach such intombment 

 accidentally if at all. The manner in which remains of land animals 

 reach the waters, in the sediments of which they become into mbed, is by 

 accidentally falling into those waters and sinking there, or into tribu- 

 tary streams which transport them to the intombing sediments, their 

 transportation being sometimes facilitated by buoyant gases which 

 accumulate in recently dead bodies. Furthermore, the annual freshets 

 which sweep the flood plains of rivers transport to such a sedimentary 

 intombment remains of the various animals which at other times safely 

 dwell there. Plant remains reach such intombment in similar ways, 

 and also by the action of the winds. In the latter class of cases they 

 are in the form of leaves and small fragments of the plants which grew 

 in the vicinity of bodies of water. Besides the methods just mentioned 

 remains of both animals and plants not unfrequently become intombed 

 in the slime and flood accretions of marshes. 



It will be shown on following pages that the difference in the condi- 

 tions under which the various kinds of fossil remains have been pre- 

 served has much significance to the geologist, but it is proper to remark 

 here that the more quiet the prevailing physical conditions and the less 

 the necessity for the transportation of those remains to reach sediment- 

 ary intombment the more likely were they to become fossilized and pre- 

 served in a favorable condition for study. The conditions presented by 

 an open seacoast were specially unfavorable because of the constant 

 triturating action of the waves. It is doubtless mainly for this reason 

 that so few remains of land animals and plants are found in marine 

 deposits, notwithstanding the comparatively abundant opportunity that 

 such remains must have had of being cast into marine waters. 



It is of such aqueous sediments as have just been referred to that the 

 stratified formations of the earth are comrjosed, and it is such remains 

 of animals and plants as have just been mentioned that constitute the 

 fossils which are found to characterize them. 



The statements which have just been made indicate that some kinds 

 of the animals and plants which existed informer geological epochs 

 could not have become represented by fossil remains in the sedimentary 

 formations, because no part of their bodies was fossilizable. They also 

 indicate that of those which might have become thus represented the 

 representation of some of them is necessarily less complete than is that 



