578 HENR V SHALER WILL I A MS 



kind of enduring power which inheres in the race itself. This 

 enduring power of organisms, expressed by the repetition of like 

 characters in successive fossil forms, is the time quality which 

 has already been used by geologists in making correlation of 

 formations by fossils, and to which we must look for the making 

 of a scientific time-scale. 



In order to isolate this time quality I have proposed to speak 

 of it as the bionic quality or value of the organism. The bionic 

 quality of a?i orga?iism 7nay, the7i, be defined as its quality of continu- 

 i?ig^ and repeating ifi successive generatiojis , the same ?norphologic 

 characters. In the case of the unit individual, it is the conti7iuing 

 of the characters, since biologically the use of parts wastes them ; 

 and only as they are renovated may they be said to continue ; 

 the active organs are here alone under consideration, for the 

 inactive hard parts are biologically dead parts whose endurance 

 is dependent only on absence of agencies of destruction. If, 

 now, we can discover some way of observing, recording, and 

 measuring the bionic values of fossils, we will be furnished with 

 a means of constructing a geological time-scale on a separate 

 (not to say independent) basis from the supposed time-scale 

 represented by the geologic column of successive formations. 



In the development of such a time-scale the first point to 

 notice is that the characters of orgafdsms differ i?i their bionic 

 value in direct proportion to their taxononiic rank. Thus, as we 

 have seen in the case of the Trilobites, the characters which have 

 ordinal or sub-class rank have persisted in the history of organ- 

 isms vastly longer than the characters of generic value ; and 

 these are of greater bionic value than specific characters. 



In discriminating periods in geological time we may look first 

 to the well-known categories of zoology and botany, as a basis 

 of determination of the order of rank in the time divisions, viz., 

 the time of endurance of a specific character (or, concretely, the 

 length of time represented by the presence of the same species in 

 successive strata of the rocks) is of subordinate rank to the time 

 of endurance of a generic character. And if we should adopt 

 the name chron to apply to geological time-units in general, 



