772 



ALEXANDER N. WINCH ELL 



Lane's gabbro aplite differs in its norm from the orthoclase gabbro 

 of Duluth by a greater abundance of quartz, and also by a greater 

 proportion of alkalies as compared with salic lime. His porphyritc 

 (VI), on the contrary, belongs to the same type (andose) as the 

 orthoclase gabbro. His porphyrite (No. i) is a beerbachose; the 

 others belong to the classes, hessose and auvergnose, so well repre- 

 sented in the Keweenawan. 



The analyses published by A. N. Winchell in 1900 were recalcu- 

 lated by Washington with the exception of that of the troctolite, the 

 norm of which is: or 2.22, ab 7.86, an 28.63, ne 5.11, di 5.91, 

 ol 30. 21, mt 10.67, il 4.41, MnO 0.08, H^O 5.23. 



In view of the scarcity of analyses of the typical volcanic rocks 

 of the Keweenawan the following new analyses are of much interest. 

 They were made by George Steiger in the laboratory of the Survey. 



ANALYSES OF KEWEENAWAN DIABASE 



* Olivine diabase from Bed io8, Eagle River section, Greenstone Cliff, Keweenaw Point, Mich 

 Sample No. s of Rohn's collection of Lake Superior rocks. Rock powdered to pass a loo-mesh sieve 

 before analysis. 



f'Ashbed" diabase from Bed 65, Eagle River section, Keweenaw Point, Mich. Sample No. 

 of Rohn's collection of Lake Superior rocks. Rock powdered to pass a loo-mesh sieve before analysis, 

 thus improving the accuracy of the figures for ferrous iron and water. 



Recalculation of these analyses on the basis of the quantitative 

 classification wives the followinsf norms: 



