510 A TREATISE ON METAMORPHISM. 



Table IV. — Analyses of fresh and altered diorite, pyroxenite, and argillite. 



One of the best cases of complete decomposition known to me is that 

 of the diabase of the iron-bearing formation of "the Penokee-Gogebic district. 

 In this rock in its most altered form not one vestige of any original mineral 

 was discovered with the microscope. While the analyses of this rock are 

 here inserted, it was largely altered below the level of ground water, but at 

 a point where abundant descending waters from the belt of weathering were 

 converged, and where therefore the conditions were intermediate between 

 those of the belt of weathering and those of the belt of cementation. The 



