3G8 Prof. J. Joly on the 



The parallel suggested by Sederholm with the Lake 

 Superior rocks is as follows: — 



Jotnian equivalent to Keweenawan. 



Jatulian „ Animikian or Upper Huronian. 



Kalevian „ 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 sub- 

 ordinate 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- 

 formably overlying metamorphosed sedimentary and volcanic 

 series — which again is divided by unconformities — is a sig- 

 nificant feature observed in many widely separated parts of 

 the world. 



The above cited facts seem to show (1) that we are entitled 

 to commence our reckoning of the sedimentary column at the 

 base of the Algonkian ; (2) that the sedimentary deposits of 

 that epoch are probably not greater than the more or less 

 concordant observations from several localities indicate ; 

 (3) that the early sedimentation was similar in character to 

 that which proceeded in subsequent periods. 



Although much is gained if w 7 e may regard these deductions 

 as secure, it is difficult to determine any approximate time- 

 equivalent for these ancient deposits. It is true that there is 

 no reason to suppose that their derivation proceeded at a 

 different rate from more recent ones ; their rate of accumu- 

 lation, however, may have been, and, indeed, probably was, 

 quickened by less stable crust conditions, permitting more 

 localized depressions and greater concentration. The dispo- 

 sition of the earlier sediments sometimes affords evidence of 

 this. There are, again, several unconformities in the pre- 

 Oambrian succession which do not appear to be represented 

 in the known sedimentary accumulations. Van Hise and 

 Leith recognize the principal unconformity as separating the 

 Archaean from the Algonkian. Adams, how T ever, recognizes 

 one of equal significance beneath the Upper Huronian. Three 

 unconformities occur within the Algonkian. That these are 

 indicative of considerable lapses of geological time is highly- 

 probable. 



