BY L. KEITH WARD, B.A., B.B. jco 



There are, according to C. R. Van Hise, two main 

 'divisions of the Pre-Cambrian which are to be recog- 

 nised in all parts of the world where rocks of this age 

 are found (i). This twofold division is based upon the 

 essential dififerences in the lithological character of the 

 upper and lower members of the Pre-Cambrian. 



The term Archaean is now restricted to that portion, 

 of dominantly igneous origin, which constitutes the 

 "basal complex. It corresponds to the " Archaeozoic " of 

 Messrs. Chamberlin and Salisbury. 



On the other hand, the term " Algonkian " is applied 

 to those rocks the origin of which is, in the main, 

 aqueous (2). Igneous rocks are associated with these, 

 but are subordinate in amount. The term Algonkian 

 • corresponds to the " Proterozoic " of Messrs. Chamber- 

 lin and Salisbury. 



This subdivision of the Pre-Cambrian into these two 

 groups has not, however, met with universal acceptance. 



In the light of the more recent researches in the 

 North American region, doubt has arisen in the minds 



■ of the Canadian geologists as to the value of lithological 



■ character alone as the basis of correlation. 



Professor F. D. Adams, in a recent paper (3), sug- 

 _gests the use of epochs of diastrophism in the compara- 

 tive study of the Pre-Cambrian rocks of North America 

 and Asia, with a view to correlation. 



In this paper Professor Adams shows that there are 

 " three major periods in the Pre-Cambrian history of 

 Laurentia, separated by two critical periods of diastro- 

 phism " (4). Of these breaks, the lower coincides with 

 that which separates the Algonkian from the Archaean; 

 while the upper break divides the Middle Huronian from 

 the Upper Huronian (Animikean). 



(i) United States Geological Survey, Bulletin No. 86. Also 

 Journal of Geology, Vol. XVII., No. 2, 1909, pp. 97-104, 118- 

 122. 



(2) It is interesting to note that the late M. A. de Lap- 

 parent brought this upper division into his Palaeozoic group, 

 calling it the Pre-Cambrian system. Below the Palaeozoic 

 group he places the Archaean group. Traits de G>5ologie, 1906, 

 Vol. II., pp. -/^z, 752-765. 



(3) Journal of Geology, Vol. XVII., No. 2, 1909, pp. 105- 

 118, 122-123. 



(4) Loc. cit., p. 115. 



