CHAPTER II. 



DESCRIPTIVE CATALOGUE OF THE ROCKS REFERRED TO IN THIS REPORT. 



Without a special description of the various beds of rock in the Lake Superior 

 region, from the micaceous and talcose schists up to the latest sandstone deposits, it 

 would be impossible to give anything like an accurate account of the beds of meta- 

 morphosed and volcanic rocks, of immense thickness, which are distributed along 

 the Lake shore, between St. Louis River and Pigeon River, and which extend 

 inland as far as the water-shed which separates the waters of Lake Superior from 

 those of Hudson's Bay. And it would be equally impossible to describe, intelligibly, 

 these metamorphosed beds without giving, at the same time, a special description 

 of the various trap dikes, of different composition, and of different ages, by which 

 they are traversed, and which have given rise to the most extraordinary reactions 

 between the sedimentary and intrusive rocks, differing in degree and effect accord- 

 ing to their composition, and to the accidents of time and association. 



In describing the Geology of the District, then, it will be necessary to describe 

 each rock individually, as it occurs at different localities. Without such specialities 

 we cannot generalize, and without a generalization of all the facts collected, no 

 comparison of this with similar regions can be made, nor can any useful addition to 

 our previous knowledge of such formations be hoped for. 



In order to avoid, as much as possible, the frequent repetitions which would 

 otherwise necessarily occur in succeeding chapters, the rocks will be referred to, in 

 the details of sections and localities, by the numbers attached to them in the follow- 

 ing catalogue. 



In describing the rocks, such terms will be employed as are usually applied by 

 geologists to the same or similar compounds ; although it must be confessed that the 

 application would occasionally be found very uncertain, if tried by a systematic 

 rule; for the metamorphosed beds of Lake Superior present almost numberless 

 undefined varieties. 



1. Greenstone — gray, compact, fine-grained; occasionally jointed; exposed sur- 

 faces iron-shot ; presents the general characteristics of the greenstone ridges north 

 of Lake Superior. 



