BASIS OF PRE-CAMBRIAN CORRELATION 27 



In Professor Van Rise's presidential address he has referred to the succession 

 of the pre-Cambrian rocks in Scotland, Finland, and China as determined by 

 Geikie, Sederholm, and Bailey Willis, respectively, and notwithstanding the fact 

 that in these successions from one to six unconformities exist, he has in each case 

 selected one unconformity as of paramount importance, and correlating this with 

 the break at the summit of the Keewatin in North America, has held that these 

 various successions support a dual division of the pre-Cambrian rocks which 

 he has maintained to be world-wide. He closes his address as follows: "I wish 

 to express my firm belief that the dual division of the pre-Cambrian into two great 

 groups of rocks [Archaean and Algonkian] seems now as firmly established as 

 the division between any other two groups." I feel, as stated in the paper, that 

 in this conclusion an "unwarranted satisfaction" is expressed. 



To sum up, therefore, it seems that the division of the pre-Cambrian rocks 

 of Laurentia into two great major divisions — Archaean and Algonkian — is not 

 supported by the facts in our possession. The pre-Cambrian succession is 

 apparently rather threefold, which three divisions may, for convenience, best be 

 designated as Lower, Middle, and Upper (Eo- Meso- Neo-) Proterozoic, quite 

 independent of any consideration of the presence or absence of life. 



