RELATION OF BIOLOGY TO GEOLOGICAL INVESTIGATION. 249 



enforcement. It is well known that such influence has at various times 

 and in various ways retarded the progress of geological science and 

 that there is danger of its being exercised in all cases when the per- 

 sonal judgment of an observer is liable to be modified or controlled 

 by official or other temporary authority. 



The opinions which have been referred to as the result of inherited 

 errors are mainly those which relate to the application of biology to 

 systematic geology. They are evidently due to the difference of ability 

 or of inclination among the authors who have written upon those sub- 

 jects, to adjust the early methods of thought which they have adopted 

 to those which were made necessary by the great revolution in the 

 views of naturalists upon the subject of evolution, which took place 

 after standards for both biology and geology had been formulated and 

 generally adopted. I regard this cause as being so important that I 

 have arranged the discussions of the geological scale now in use so 

 that they embrace references to the condition of thought among pro- 

 moters of geological science from about 25 years before the revolution to 

 the present time. 



It is apparent, however, that, besides, the tendency to follow estab- 

 lished channels of thought, which has just been referred to the contin- 

 uance of these differences of opinion, and the consequent differences in 

 practice among geologists, are largely due to the fact that the princi- 

 ples and criteria which are necessary to constitute a standard or series 

 of standards which shall accord with modern views of biology have 

 never been conventionally formulated and published. It is very desir- 

 able that concerted attempts toward such formulation should be made, 

 but it is nevertheless true that the necessity for a special exercise of 

 personal judgment in every act of geological investigation renders 

 exact formulation peculiarly difficult. 



The attempts toward enunciating principles and formulating criteria 

 which are made in these essays have been suggested by those of my 

 own geological investigations which have been prosecuted mainly from 

 a biological standpoint. Among the incentives to these attempts has 

 been a desire to give to the readers of my published writings upon the 

 subjects referred to a more explicit statement of the grounds of cer- 

 tain opinions therein expressed than it was practicable to make in those 

 writings. Indeed I believe the present general condition of geological 

 science in all its departments demands from its active investigators 

 some more definite public exposition of principles, and even of certain 

 elements, than has yet been published. It is at least apparent that 

 such publications for each subordinate branch of geology would be of 

 great service to students because it would give them greater facility in 

 comprehending the meaning of authors, and it would enable the latter 

 to write more concisely and intelligibly, as well as more accurately, 

 upon the results of their investigations. It would also give authors in 

 the different branches of geology an opportunity to become better 



