PETROGRAPHY OF THE KEWEENAWAN 



651 



Pumpelly had an analysis made with similar results. Both samples 

 represented pseudo-amygdules, and the results have been widely 

 accepted, though it seems possible some other constituent may have 

 been attacked with McFarlane's chlorite. Dr. Berkey^ found the 

 chlorite amygdules of Grand Marais on the north shore of Lake 

 Superior to be strigovite. Three of the samples now tested seem to 

 be much like delessite and the fourth does not seem to be a definite 

 chlorite. The analyses, though similar to those given by Dana, are 

 quite different from earlier analyses of Keweenawan material. Those 



TABLE V 

 Analyses of Chlorite and "Green Earth" 



1. Chlorite, silky amygdules, Pine City, Minn. F. F. Grout, analyst. 



2. Chlorite pseudo-amygdules, Upper Tamarack Creek, Minn. F. F. Grout, 

 analyst. 



3. Green earth of slickensides. Crooked Creek, Minn. F. F. Grout, analyst. 



4. Green mineral from rock analyzed. Number 3, Table IV. C. F. Sidener, 

 analyst. 



* The moistxxre lost on drying at 100°, though great, was almost entirely regained after exposure to 

 ordinary air. 



were low in magnesia and high in alumina and iron oxides. The 

 high ferric oxide which has been mentioned in connection with reduc- 

 tion of copper is less prominent in these new analyses. The chlorite 

 has a hardness of about 2, and the color varies — usually green and 

 light enough so that sections are very faintly colored. The structure 



I C. p. Berkey, Minn. Geol. and Nat. Hist. Survey, Ann. Report 2J, 194. 



