390 THE CAMBRIAN. Ibull.81. 



its distinct sedimentation and fauna, is known, and no other appears to 

 have been deposited. In the Appalachian Province, in Vermont, the 

 Lower Cambrian is readily separated by organic remains and sedimen- 

 tation; bat with our present knowledge it is impossible clearly to dis- 

 tinguish between the Middle and Upper Cambrian. The same is true 

 throughout the Appalachian region, except in the Adirondack sub- 

 province, where the Upper Cambrian is well developed. In the Rocky 

 Mountain Province the Lower Cambrian is distinctly developed, but the 

 Middle and Upper merge more or less into each other. The problems 

 in this connection requiring investigation are clearer delimitations of 

 the Middle and Upper Cambriau in the Appalachian and Kocky Moun- 

 tain Provinces, both by the careful study and comparison of the sec- 

 tions and the collecting and differentiation of the faunas. 



It is not anticipated that uniformity will be found to exist in each of 

 the primary subdivisions; the sedimentation of the various provinces 

 is too unlike. The three divisions will have to be used, if at all, in a 

 somewhat arbitrary manner in some of the areas, just as the greater 

 division of the Cambrian is arbitrarily separated from the Silurian 

 (Ordovician) where no physical line of division is apparent. We recog- 

 nize the Cambrian group as a convenient means of classification, but 

 its subdivisions must be controlled by the needs of the local geologist 

 and not used unless distinctly recognize^. • 



