8 CHARLES RICHARD VAN HISE 



be frequently equated in the same geological province, as, for instance, 

 in the case of the Upper Huronian in the different districts of the 

 Lake Superior region, it has not been found practicable to equate 

 them from province to province. That is to say, one cannot be 

 certain as to the correspondence of individual Algonkian series of 

 China, Scandinavia, and of the Cordilleran region. If, as above 

 suggested, it becomes possible to work out the physical history of the 

 continents so that it may be determined which of the unconformities 

 are continental, and intercontinental, or if in the pre-Cambrian rocks 

 distinctive faunas are found, then closer correlation of the pre-Cam- 

 brian in different geological provinces may be possible than the 

 Archean and Algonkian. In the meantime we must be content with 

 the classification of the pre-Cambrian rocks in different geological 

 provinces into Archean and Algonkian, with the understanding that 

 the formations placed in each of these groups belong in a general 

 way to the two early eras of the earth, during the first of which the 

 agencies were dominantly igneous, and during the second of which 

 the conditions had become similar to those of today. Further, 

 within each geological province the Archean and Algonkian may 

 be divided into series and formations which for each province are 

 given local names. 



