RELATION OF BIOLOGY TO GEOLOGICAL INVESTIGATION. 275 



III.— THE RELATION OF FOSSIL REMAINS TO STRUCTURAL GEOLOGY. 



The character and origin of fossil remains and the character and 

 limitation of the sedimentary formations, as well as the manner in 

 which the latter originated and became fossiliferons, have been dis- 

 cussed in the preceding essays. It is necessary that such discussions 

 should have preceded those which are embraced in this and following 

 essays, because they contain numerous statements of tact which it 

 will be constantly necessary to refer to or to bear in mind in connection 

 with the subjects now to be discussed and without which those sub- 

 jects couhl not be intelligibly presented. 



There are two methods by which the study of fossils may legitimately 

 be applied to geological investigation, the following statement of the 

 character of which is in part explanatory of the results that may be 

 obtained by their aid. For convenience one of them maybe termed 

 empirical and the other philosophical, because in the one case results 

 are obtained by experience and in the other by reasoning upon the 

 various results thus obtained. Still, discrimination between these two 

 methods can not usually be sharply drawn, because while all geological 

 investigation is largely empirical it is always more or less philosophical. 

 Such a division of the subject, however, besides being a present con- 

 venience, gives me an opportunity to emphasize the fact that a large 

 proportion of the work that is done in structural geology is based 

 mainly upon the empirical observation and collection of biological data. 



Both these methods are not only important but indispensable, the 

 one not less so than the other. Both may be, and often are, used 

 together, but the empirical method is more largely used in practical 

 field studies than in others, because in such studies fossils' are to a 

 large extent treated as characteristic tokens of formations or as arbi- 

 trary means of identifying them and distinguishing them from one 

 another. Such identification necessarily constitutes one of the first 

 steps in the practical study of structural geology, but the subsequent 

 study of the fossils thus empirically used is necessarily more philo- 

 sophical. 



Furthermore, in the prosecution of field studies it is often necessary 

 to make special philosophical use of fossils, not only with reference to 

 questions which are discussed in following essays, but to some of 

 those which relate more particularly to the subject of this. Among 

 such questions are those which relate to the conditions of origin of 

 formations, the character and quality of the waters in which they were 

 deposited, and the various conditions of habitat of the faunas and 

 floras whose remains characterize them. 



The philosophical method of treating fossil remains, however, is 

 largely applicable to systematic geology or those branches which per- 



