16 C. K. VAX HISE THE PROBLEM OF THE PKE-CAMBEIAX 



the fundamental dual division of the pre-Cambrian with the group of 

 geologists that prefer the zoic terms is Proterozoic and Archeozoic. This 

 classification is adopted by Chamberlin and Salisbury in their text-book. 



The question now arises as to which pair of terms is jDreferable for 

 common use — the above, or Algonkian and Archean. The convenience 

 of the terms Algonkian and Archean to represent the two divisions of the 

 pre-Cambrian has been somewhat generally recognized, and besides ap- 

 pearing on the geological atlas of the United States and in the publica- 

 tions of American geologists, they have found favor in Europe. 



Thus Algonkian and Archean are the major divisions for the pre- 

 Cambrian found upon the official geological map of France, published in 

 1905 under Michel-Levy as inspector general and compiled by a commit- 

 tee consisting of thirty-five geologists of that country, with the assistance 

 of a committee of fifty other geologists. These committees include prac- 

 tically all of the eminent geologists of France. It is therefore safe to 

 say that the consensus of opinion of the geologists of that country, in 

 accordance with that of the geologists of the United States Geological 

 Survey, is in favor of the terms Algonkian and Archean for the primary 

 divisions of the pre-Cambrian.. 



The wisdom of the conclusions of the geologists who selected the terms 

 Algonkian and Archean for the two major divisions of the pre-Cambrian 

 has since been confirmed by considerations which have developed since the 

 adoption of the terms. As has been seen, when the terms Agnotozoic and 

 Proterozoic were proposed by Irving in the sense now conveyed by Algon- 

 kian, it was known that the rocks there placed contained positive evidence 

 of life, but it was supposed that the inferior group of the jjre-Cambrian 

 contained no evidence of the existence of life. It has since been ascer- 

 tained that in the Archean all the evidences of life shown by the Algon- 

 kian exist, with the exception of the few iiiijjerfect fossils which are now 

 known in the latter group. Thi;s there arises, if zoic terms are to be 

 used, the necessity for the introduction of another zoic term for the 

 Archean (and, as has been seen, Archeozoic has been suggested) ; or, if 

 this be not done, it is necessary to extend one zoic term to cover all of the 

 pre-Cambrian rocks to the base of the earth formations. 



The objection to a dual zoic division for the pre-Cambrian rocks is that 

 their life is not known to be different. When we say Paleozoic and Meso- 

 zoic, we understand the terms to indicate a great known faunal differ- 

 ence. We think not so much of the rocks, their lithological contrasts 

 and the differences of the physical conditions of their formation, as of 

 the life contrast. The rocks which contain a Paleozoic fauna are Paleo- 

 zoic: those which contain a Mesozoic fauna are Mesozoic. The separa- 



