280 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1911. 



mentary origin represents a departure from the uniformity of condi- 

 tions of later geological times." l 



Turning to the pre-Cambrian geology of other parts of the world we 

 find that the Torridonian and Lewisian of northwest Scotland in 

 their mutual relations and petrographical characters resemble the 

 Algonkian and Archaean divisions of North America. The aggregate 

 thickness of the Torridonian has been estimated at not less than 

 10,000 feet. To this the Dalradian has, possibly, to be added. 



The pre-Cambrian rocks of Finland have been divided by Sederholm 

 as follows : 



Jotnian. 



Jatulian, Upper. 

 Jatulian, Lower. 

 Kalevian, Upper. 

 Kalevian, Lower. 



Bottnian. 



Ladogian. 



Katarchsean. 



Sederholm makes the same statement regarding the Jotnian, 

 Jatulian, Kalevian, and Bottnian as has been made with reference to 

 the Algonkian. Sederholm says: 



At least as far back as during Bottnian time the climatic 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 themselves to be sediments with the 

 same regular alternation of clayey and sandy material (annual stratification) as the 

 glacial clays of that same region, explainable only by assuming a regular change of 

 seasons. 2 



The parallel suggested by Sederholm with the Lake Superior rocks 

 is as follows : 



Jotnian equivalent to Keweenawan. 



Jatulian equivalent to Animikian or Upper Huronian. 



Kalevian equivalent to Lower Huronian. 



Van Hise and Leith further suggest the correlation of the Ladogian 

 and Katarchsean with the Kewatin and Laurentian; the Ladogian 

 being intruded by the granites and gneisses of the Katarchsean. 



In China a basal complex of gneisses having very subordinate masses 

 of sedimentary materials underlie four sedimentary groups, originally 

 muds, grits, conglomerates, and limestones; having, in fact, all the 

 characteristics of the Algonkian. In short this prevailing relation 

 of an older gneissic and dominantly igneous system with an uncon- 

 formable overlying metamorphosed sedimentary and volcanic 



i Van Hise and Leith, loc. cit., p. 30. 



5 Sederholm, J. J., Bull. Comiu. Geol. de Finlande, No. 23, p. 95, 1907. 



