PKE-CAMBRIAN OF FINLAND 25 



From this succession it appears that in Finland there are at least four 

 pre-Cambrian sedimentary series. For the Jotnian, Jatulian, Kalevian, 

 and Bottnian, Sederholm makes exactly the same point as has been made 

 with reference to the Algonkian. He says : 



"At least as far back as during Bottuian time, the climate conditions were 

 not sensibly different from those of later geological periods, as shown by the 

 existence of rocks, which in spite of their metamorphic character show them- 

 selves to be sediments with the same regular alteration of clayey and sandy 

 material ('annual stratification') as the glacial clays of that same region, ex- 

 plainable only by assuming a regular change of seasons."^* 



He further says that the prol)lem of the pre-Cambrian stratigraphy has 

 been solved "in a decidedly actualistic direction." While Sederholm is 

 too cautious to make any definite correlations with the Lake Superior 

 region, he suggests that the Jotnian is similar to the Keweenawan of 

 North x\merica, the Jatulian equivalent to the Upper Huronian (Ani- 

 mikie), and that the Kalevian is perhaps similar to the Lower Huronian 

 of North America. This suggested likeness is even greater when it is 

 remembered that what was originally called the Lower Huronian is now 

 divided into the Middle and Lower Huronian, and that the Kalevian is 

 divisible into two imconformable series. 



These sedimentary series together constitute the Algonkian. Uncon- 

 formably l)clow these are two series of rocks, the upper called the Lado- 

 gian, and this series is intruded by the granites and gneisses of the 

 Katachean. Thus Finland lias the two divisions of the Archean which 

 correspond to the Keewatin and Laurentian. The only essential differ- 

 ence is that in the Ladogian, equivalent in position to Keewatin, the sedi- 

 mentary rocks seem to be more important relatively than in America. 



It is plain that the major dual classification of the rocks of Finland 

 into Archean and Algonkian is justified. 



CHINA 



In China the work of Richthofen showed that the pre-Cambrian rocks 

 have an extensive development, and some of tlie sediments here belonging 

 he tentatively correlated with the Huronian. The recent work of Willis 

 and Blackwelder has placed the pre-Cambrian stratigraphy of northern 

 China on a systematic basis. 



According to Willis," "A provisional classification of the Wu-t'ai and 

 limiting systems in the type locality is as follows:" 



" Op. cit.. p. 95. 



'•'Research in China, vol. ii, Systematic Geology, by Bailey Willis, p. 4. 



Ill — BULU Geol. Soc. Am., Vol. 10, 190T 



