2X4 REPORT OF NATIONAL MUSE I'M, 1892. 



IV. THE RELATION' OF BIOLOGY T< > SYSTEMATIC AND HISTORICAL 



GEOLOGY. 



The preceding essay was devoted to discussions showing the im- 

 portance of all fossil remains as well as the interrelative value of the 

 different kinds of the same in the prosecution of geological field work. 

 A leading object of that essay was to show that fossils constitute 

 the most important of the distinguishing characteristics of all sedi- 

 mentary formations and also the principal means of their identifica- 

 tion as physical units of stratigraphic classification within any district 

 or region. This essay is devoted to discussions of the more general 

 relation of fossil remains to geological investigation; that is, to general 

 discussions of the relation of biology, the science which they, together 

 with living animals and plants, represent, to certain of the broader 

 subjects of geological study. These subjects embrace systematic ge- 

 olgy, or the general classification of the stratified rocks of the earth, 

 historical geology, or the establishment of that classification upon a 

 chronological basis, and correlative geology, or the adjustment to one 

 another of the full chronological series of stratified rocks which occur 

 on each continent or large division of the same. The latter subject, 

 however, will be more specially discussed in Ess;iy vi. 



It has been made apparent in the preceding essays tliat each case 

 of structural classification of stratified rocks based upon formations as 

 physical units is independent of all others, and that its application is 

 necessarily of limited geographical extent, because formations are them- 

 selves thus limited. It therefore follows that the structural geology 

 of any district or region, embracing even an extensive series of forma- 

 tions, may be practically and thoroughly investigated, as regards both 

 scientific accuracy and economic requirements, independently of that 

 of any other district or region, especially of those regions which are 

 not adjacent. It is now to be shown how the multitude of series of for- 

 mations thus locally classified throughout the world have been grouped 

 into a universal system of classification in connection with a scale hav- 

 ing its divisions arranged in chronological order. 



The grandest and most comprehensive of the ideas which were con 

 ceived and developed by the early geologists relates to the construc- 

 tion of this scale and the conserpient reduction of geology to a, univer- 

 sal system; but it is remarkable that although this idea is now known 

 to have an almost exclusively biological basis, its original conception 

 was not the result of correct biological knowledge as now understood, 

 but of empirical observation of physical and biological facts and a 

 sagacious perception of their interrelation. 



It is true that while the early geologists relied mainly upon fossils as 

 indicators of the relative age of formations, the belief was at first 



