Lower or Archaean < 



86 EDWARD STEIDTMANN 



segregations. The richest ores contain about 60 per cent iron. 

 They are not used at present because of their titanium content, 

 excepting on a very small scale. Their extent is unknown. In the 

 Lake Sanford district alone, 90,000,000 tons are known. 



Karl L. Herming^ reviewed the principal results of Van Hise and 

 Leith's Pre-Cambrian Geology of North America. 



Kemp^ states that the following tentative chronologic table of 

 the Swedish pre-Cambrian based on the work of Sederholm and 

 Hogbom is finding favor : 



f Epijotnian dislocations 

 Upper or Jotnian \ Jotnian 



I Subjotnian land surface denudation and igneous rocks 

 f Epijatulian folding 

 Middle or Jatulian \ Jatulian 



[ Subjatulian land surface and denudation 

 ' Serarchaean granites 

 Archaean 



No chronological subdivision. Difference due to vary- 

 ing metamorphism 



Kemp shows that the Archaean of Sweden is separable into two 

 major divisions, an older complex of minor sediments and major 

 deep-seated intrusives, and a younger series of intrusive granites 

 consisting of four distinct types. Similarly, the Archaean of the 

 Lake Superior region embraces an older division consisting of minor 

 sediments and major igneous rocks, mostly basic extrusives, how- 

 ever, and a younger division consisting almost entirely of granitic 

 intrusives. The sediments of the Swedish Archaean contain 

 squeezed conglomerates, crystalline Hmestones and dolomites, mica 

 schists, leptites, garnet, cordierite, silUmanite, and graphite gneisses 

 of probable sedimentary origin. The leptites are fine-grained, 

 banded, and stratified rocks, which include sediments and iron ores. 

 The Archaean sediments of the older division in the Lake Superior 

 region include iron formation and minor elastics. The Archaean 

 igneous rocks of Sweden of the older division comprise granites, 

 gneisses, and gneissoid intrusives, titaniferous ore-bearing gabbros, 



'Karl L. Henning, "Die pro-kambrische Geologic von Nord Amerika," Natur- 

 wissenschaftUche Wochenschrift, N.F., Bd. No. 28 (July, 1910), pp. 433-37- 



^ J. F. Kemp, " Comparative Sketch of the pre-Cambrian Geology of Sweden and 

 New York," New York State Museum Bull. 149, 1910, pp. 93-119. 



