DELATION OF BIOLOGY TO GEOLOGICAL INVESTIGATION. "-V.> 



changes in the contemporaneous land fauna and flora; Therefore it is 

 to* be assumed that such faunas and floras in their entirety bore an 

 important indirect relation to the respective formations with the pro- 

 duction of which they were contemporaneous, and that such of their 

 remains as found intoinbment in their sediments would be largely 

 characteristic of them. 



Still, the incongruity of the biological relation and of the physical 

 conditions of existence of land faunas and floras to aquatic faunas* 

 and the accidental relation of such of the remains of the former as 

 became fossilized to the sediments in which they were intombed render 

 it difficult to treat the evidence afforded by fossils of terrestrial origiU 

 as concurrent with that which is afforded by aquatic fossil faunas. This 

 difficulty is increased by the incompleteness of representation by fossil 

 remains of land animals as entire faunas, and that of plants not only as 

 entire floras but as individual members of them. 



Furthermore, remains of land animals and plants have never been 

 found in any of the fossiliferous formations of the earlier geological ages, 

 and in the marine formations of the later ages* they are rarely, and 

 usually never, found.t Therefore their study, except in cases of doubt- 

 ful value, is confined to the nonmarine formations of the carboniferous 

 and later ages. The restricted range of such studies as compared with 

 that of the study of other fossils is the more apparent when it is remem- 

 bered how small is the proportion of non marine to marine formations. 

 These remarks are by no means to be understood as suggesting the 

 rejection of any kind of evidence in any case or as calling in question 

 the general paleontological, and the purely biological, value of fossil 

 remains of terrestrial origin. It is only claimed that their value in the 

 characterization, identification, and limitation of formations is below 

 that of remains of aquatic faunas. 



It was also mentioned in the preceding essay that the biological 

 characterization of any formation is fully recognizable only by means 

 of its fossil fauna or flora, each as a whole, and not by separate mem- 

 bers of either, although separate members, especially of an aquatic 

 fauna, because of their limited vertical range, are often sufficient for 

 its identification after its characterization has been fully established. 

 This fact is of importance in every estimate of the true value of fossil 

 remains in practical geology, because, notwithstanding their paramount 

 value as evidence in the cases referred to, no evidence in such cases is 

 ever so complete as to be beyond the need of accessory support. 



The foregoing remarks apply to that direct practical use of fossils 

 which is necessary from the beginning to the close of every investiga- 

 tion of structural geology. The following apply to their more indirect 

 use in reaching conclusions of a general character, but which are also 



* See table on Plate xiv, showing time ranges of animals and plants. 



t Diatomaceons remains are not considered in connection with this statement. 



