﻿262 R. D. Irving — Ferruginous Schists and 



number of points. Throughout most of this distance, the basal 

 beds of the series, or at least the lowest beds in sight, are highly- 

 ferruginous and include nearly if not quite all of the lithologi- 

 cal kinds with which we are now concerned. At some points 

 but one or two of the kinds are to be seen, but at others most 

 of them occur together in intimate association, and the whole 

 appearance is such as to render in the highest degree probable 

 a common origin for all the phases; a probability which is 

 carried to demonstration by a study of the thin sections, which 

 present us with complete gradations from the unaltered car- 

 bonates to cherty and jaspery materials, and even to actinolitic 

 magnetite-schists. 



A fine showing of the least altered form of these ferruginous 

 rocks is to be seen on the Kaministiquia River, at Kakabika 

 Falls, Canada, where there are black slates interbedded with 

 bands of dark-gray to light-gray carbonate. Complete analyses of 

 these two varieties, made in the laboratory of the Geological 

 Survey, show a content of siderite ranging from 35-45 per 

 cent. The fact that even the black slate contains at times as 

 much as forty per cent of siderite in the mass of the rock cer- 

 tainly seems to prove, as does the whole appearance of the 

 large exposure, the original character of the carbonate. In 

 both places carbonaceous matter is present, the content of car- 

 bon in the black slate reaching 3*54 per cent. Besides the 

 carbonate and organic matter, there are present clayey material, 

 a small quantity of magnetite, and a considerable quantity of 

 silica. The latter is present to a slight extent as fragmental 

 quartz, but a very much larger part has evidently separated 

 out in its present position. This ranges from a mosaic of finely 

 crystalline quartz, through chalcedony, to amorphous silica. 

 Most of this silica is manifestly of a secondary origin, but some 

 of the more amorphous material may date from the original 

 solidification of the rock. 



The showing on the northern sides of Gunflint and North 

 lakes, on the national boundary line, is, however, of much 

 greater interest in the present connection. Here the alteration 

 has been carried much further, and bands of the carbonate are 

 found interleaved with seams of magnetite and others of a 

 chalcedonic to cherty silica, and still others of a jaspery ma- 

 terial, in which case bands of specular iron are included within 

 the jasper. On the northern side of JSTorth Lake this jasper 

 reaches an immense development, forming bold cliffs facing to 

 the northward. The magnetitic slates on Gunflint Lake are 

 highly charged w T ith actinolite and tremolite, and a study of the 

 thin sections seems to make it manifest that all of the varieties 

 have proceeded from a silicification of the carbonate, every 

 stage of the transition being met with from the carbonate to 



