REPORT OF THE DIRECTOR 1920-21 79 



Prof. J. F. Kemp (191 1) after becoming personally acquainted with 

 the Precambrian geology of Scandinavia at the occasion of the elev- 

 enth International Geological Congress, has compared the American 

 and Scandinavian series of Precambrian rocks and expressly com- 

 mented (op. tit., p. 105) on the profound impression of similarity and 

 resemblance " that remained in the minds of the Americans, not- 

 withstanding some differences "; adding, "so much so, that when 

 in the field the Americans in the end became embarrassed at their 

 constant and almost irrepressible tendency to remark upon it to 

 their Swedish hosts." The table given by Kemp (p. 95-105), 

 after the works of Hogbom and Sederholm, shows an almost iden- 

 tical succession of rocks and diastrophic events in the Scandinavian- 

 Finnish and American Precambrian series. Over there are dis- 

 tinguished as main divisions or eras, the Archean, Jatulian and 

 Jotnian, which going downward in the progressive development of 

 metamorphism and general crustal unrest, as well as their lithologic 

 characters, closely correspond to the American series. The Archean 

 is there, as here, closed by a period of huge granite intrusions (the 

 Post-Bottnian or Serarchean granites) and intense diastrophic 

 activity, followed by a long interval of erosion. Likewise the Jatulian 

 era is closed by a period of strong mountain-folding and much 

 volcanic activity, which produced the peculiar Rapakivi granites, 

 by final elevation and land surface denudation (" epi jatulian folding " 

 and " sub jotnian land surface denudation and igneous rocks"). 

 The Jotnian, finally, is compared by Kemp with the Torridonian 

 of Scotland and the Keweenawan of the Lake Superior region. Like 

 the latter, the closing stage of the Proterozoic in America, it is more 

 local in its development and distribution as compared with the 

 Archean and Agnotozoic rocks. 



In regard to the Asiatic Precambrian nucleus, Bailey Willis (1907, 

 v. 2, p. 4) has shown a succession that is also divided by two major 

 unconformities into three systems that exhibit progressive meta- 

 morphism, volcanic intrusions and diastrophism in a downward 

 direction. Adams (1908, p. 117) states in regard to a correlation of 

 this Asiatic Precambrian with the American: " Applying therefore 

 this criterion of diastrophic periods to the correlation of the Pre- 

 cambrian succession of these widely separated portions of the great 

 northern nucleus we obtain an identical result in both cases, the 

 diastrophic movements seem to have affected the nucleus as a whole." 

 (italics ours). 



While in none of the other large Precambrian massifs the presence 

 of two major unconformities, beside several smaller ones, has, p. 80, 



