644 



FRANK F. GROUT 



understand how a matrix of the composition of augite should develop 

 first some large crystals of that mineral, and later a glass of the same 

 composition. The chlorite-like mineral which Pumpelly refers to 

 glass, is admitted to be with difficulty distinguished from other chlorite 



in the rock, 



TABLE I 

 Analyses of Mottled Diabases 



1. Original type locality, Greenstone of Keweenaw Point, Mich. George 

 Steiger, analyst. Journal of Geology, XVI, 765. 



2. Taylors Falls, Minn., along railway track. F. F. Grout, analyst. 



3. Tamarack Falls, Tamarack Creek, Pine Co., Minn. F. F. Grout, analyst. 



4. Upper Tamarack Creek, Minn. Weathered red. A. W. Johnston, analyst. 



5. Upper Tamarack Creek, Minn. Weathered green. A. W. Johnston, analyst. 



* For the significance of these names see Journal of Geology, X, 555. 



The alteration was Pumpelly's special study^ and proved interesting 

 and complex. For details of the several successive changes, refer- 

 ence must be had to the original. The chloritic minerals are of 

 greatest interest, and their nature is variable in each of the several 

 types of occurrence, as shown below. 



I R. Pumpelly, Proc. Am. Acad. Arts and Sciences, XIII, 253. 



