190 



GEOLOGICAL BIOLOGY. 



the characters reaching a greater prominence and constituting 

 the marks of another higher group, and then they constitute 

 distinct generic characters. 



This theory of the origin of species accounts for the 

 morphological appearance of the new species by supposing 

 that the future specific characters were first in the state of 

 simple varietal modifications of the parental forms, and be- 

 came fixed and permanent in the course of regular develop- 

 ment in the whole or a part of the members of the descended 

 race. Those members of the race permanently developing 

 the new characters constitute the new species. 



The varietal character may be algebraically expressed as 

 either a plus or minus quantity; i.e., the variety may differ 

 from the typical species by the addition of some slight char- 

 acter, or by the absence of some character, possessed by the 

 normal species. 



Characters of any Particular Specimen Differ Greatly in 

 Antiquity. — In regard to the antiquity of the characters the 

 following facts are known, as expressed in the following table: 



TABLE REPRESENTING THE VARYING ANTIQUITY AND DIFFERENT GEO- 

 LOGICAL RANGE OF THE CHARACTERS OF AN EXAMPLE OF THE 

 SPECIES SPIRIFER LOGANI HALL. 



The varietal characters, expressed by the name Spirifer 

 Logani Hall, appeared geologically for the first time in the 

 Keokuk limestone in Middle Eocarboniferous time in North 

 America. The specific characters, represented by the specific 



