SOME PRE-CAMBRIAN LITERATURE OF NORTH AMERICA 87 



syenites, and anorthosites. The leptites, sediments, and iron ores 

 are compared by Kemp to channels amid an archipelago of large 

 island intrusives. 



The surface on which the Jatulian was deposited is regarded as 

 hilly by Hogbom and mountainous by Tornebohm. Kemp believes 

 that the time gap of erosion which separated the JatuHan from the 

 Archaean was not so long as the one which separated the Cambrian 

 from the Jotnian or the Jotnian from the Jatulian. The Jatulian 

 in Sweden consists of quartzite, schists, dolomitic Hmestones, and 

 beds of anthracite, which have a maximum thickness of two meters. 



Professor Sederholm has divided the Jatulian of Finland into an 

 upper and lower member which consist of eruptives, greenstones, 

 elastics, and dolomites, and has compared it to the Upper Huronian 

 of the Lake Superior region. The Jatulian closed with a period of 

 very intense folding, followed by intrusions of a peculiar porphyritic 

 granite which decomposes readily, forming the so-called rapakivi, 

 Finnish for rotten stone. This has afforded an important guide by 

 which Swedish geologists have measured the age of various other 

 intrusives and metamorphic rocks. The erosion which followed 

 developed an even floor free from weathering products, on which 

 the Jotnian diabases and ripple-marked and sun-cracked sandstones 

 were deposited. These now lie in isolated patches. They are com- 

 pared by Professor Kemp to the Torridonian of Scotland and the 

 Keweenawan of the Lake Superior region. Finally, Cambro- 

 Silurian sediments of which widespread relicts remain were de- 

 posited upon a generally even surface covered with a weathering 

 breccia which grades downward into a kaolinized gneiss. So-called 

 sandstone dikes containing Cambrian fossils are found in gneisses 

 far from Cambrian beds. 



Most of the comparisons made by Professor Kemp between the 

 pre-Cambric of Sweden and New York are necessarily petrographic 

 and appeal to those who are personally familiar with the rocks of 

 the New York pre-Cambrian. 



Lane^ finds that the grain of Laurentian granites tends to be 

 uniform from the margin to the center, from which he infers that 



^ A. C. Lane, "The Stratigraphic Value of the Laurentian," Compte Rendu, 

 XI. Congres Geologique International, 1910, pp. 633-37. 



