42 C. D. Waleott — Position of the Olenellus Fauna. 



of the Ordovician fauna has been in the direction of differenti- 

 ating the class types that existed in the earlier fauna with one 

 or two exceptions, the most notable of which is the Cephalo- 

 poda. The classes represented by non-testaceous species may 

 or may not have existed. 



The study of the Olenellus fauna adds a little more to our 

 knowledge of the rate of convergence backward in geologic 

 time of the lines representing the evolution of animal life 

 and at the same time proves that an immense time interval 

 elapsed between the beginnings of life and the epoch repre- 

 sented by the Olenellus fauna. 



The study of the Olenellus and Middle Cambrian faunas 

 illustrates very forcibly the strength and weakness of paleonto- 

 logical correlation. To the student reading this paper it may 

 appear that the correlation is based on a correspondence in age, 

 whereas, it is the homotaxis or similarity of order that is used 

 in correlating the widely separated portions of the Olenellus 

 fauna. It is the expression of the similarity of serial relation 

 in the faunas contained in the strata of different provinces or 

 areas. We cannot state that the Olenellus fauna of Sweden, 

 New York and Nevada was contemporaneous in time, but we 

 can state that the relations of this fauna to the succeeding 

 Middle and Upper Cambrian and Ordovician faunas is essen- 

 tially the same in the widely separated localities. Also that 

 the Olenellus fauna is the basal fauna wherever it has been 

 found. 



As an element of weakness in paleontologic correlation, we 

 may cite the character of the Middle Cambrian or Paradoxides 

 fauna of the Atlantic Province as compared with the essen- 

 tially different Middle Cambrian fauna of the Rocky Mountain. 

 Province. The position of the latter in the geologic series 

 would not be inferred from its zoologic characters. It is only 

 its occurrence at an horizon between the Lower and Upper 

 Cambrian faunas that gives any strong reason for correlating it 

 with the Paradoxides fauna. The latter retains all the essen- 

 tial characters of the Primordial fauna whereas the former 

 partakes in its trilobites largely of the characters that are more 

 typical of the Ordovician fauna. It appears from what we 

 now know of the two, that the Middle Cambrian fauna of the 

 Rocky Mountain Province had advanced further in develop- 

 ment toward the Ordovician fauna than had the Paradoxides 

 fauna of the Atlantic Province. It is an interesting fact in 

 this connection that the Upper Cambrian fauna of the Rocky 

 Mountain Province and the Atlantic Province appears to be 

 essentially of the same grade or phase of development. What 

 became of the descendants of the Middle Cambrian fauna of 

 the Rocky Mountain Province during Upper Cambrian time is 

 one of the unsolved problems. 



