104 CHARLES RICHARD VAN HISE 
geological provinces may be divided into two or more series separated 
by unconformities. The formations of these series are commonly 
sedimentary, although igneous rocks are often abundant. As a whole, 
to the Archean group ordinary stratigraphical methods do not apply. 
To the Algonkian such methods are as applicable as to the Paleozoic 
and later series. 
While the subdivisions of the Archean and of the Algonkian can 
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. 
