358 C. W. HALL — KEEWATIN OF EASTERN AND CENTRAL MINNESOTA 



ship between (1) well defined ora3^wackes and graywacke-slates, (2) 

 biotitic graywackes, (3) biotite- schists and muscovitic biotite-schist of 

 the Penoked Gogebic range as a graded series from the slightly altered 

 gra3Mvackes to the cr3''stalline mica-schists, this relationship being for- 

 mulated in the following proposition : 



"the result bein^ the production from a completely fragmeutal rock, by meta- 

 somatic changes only, of a rock which presents every appearance of complete 

 original crystallization, and which would be ordinarily classed as a genuine crys- 

 talline schist." * 



« 



At nearl}^ the same time Lawson worked out the relationship between 

 the elastics and schists of the Raiii}^ Lake and Lake of the Woods region 

 and stated his results.f showing that the granite of the region is of later 

 origin than the folded schists, and that the period of folding occurred 

 at a date earlier than that of the deposition of the typical Huronian of 

 Logan — that is, the Animikie.J 



Two years later Lawson, § in stating the results of liis studies around 

 Rainy lake, says with reference to one })articular locality, that the de- 

 trital origin of the series of fissile soft green chloritic and hornblendic 

 schists is established through their forming the paste of a pebble-and- 

 boulder conglomerate (page 83 F), and touching another locality he 

 says (page 84 F) that the matrix of a conglomerate is a more or less 

 calcareous, decomposed schist. 



Again, in the Black hills of South Dakota, a region to be associated 

 genetically with that extending from lake Superior southwestward, 

 within which lies the district under discussion. Van Hise observed || that 

 slates, quartzites, and conglomerates occurring in a broad central belt 

 become more crystalline and grade into schists about the volcanics to 

 the north and the granite of Harney peak to the south, " In the transi- 

 tion in both directions, graywacke-slates change into mica-slates, the 

 mica-slates into non-foliated mica-schists, the non-mica-schists into 

 foliated mica-schists (which are both garnetiferous and staurolitic) and 

 even into gneisses." 



HISTORICAL NOTES 



The group of rocks around Thomson and Carlton, as has already been 

 stated, have long been considered elastics in origin. In a vague sort of 



* Loc. cit., p. 454. 



t A. C. Lawson : Report on the Geology of the Lake of the Wood.s, Ann. Rept. Geol. and Nat. Hist. 

 Survey of Canada, 1886, pp. l-151cc. 



X Loc. cit., p. 1.3. 



gGeol. and Nat. Hist. Survey of Canada, Ann. Kept., new series, vol. iii, pt. i, report F, pp. 1-190. 



II C. R. Van Hise : The pre-Cambrian rocks of the Black hills, Bull. Geol. Soc. Am., vol. i, 1890, 

 pp. 203-243. Quotation is from p. 223. 



