126 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
SEotion IIL—SUMMARY VIEW OF THE ORIGINAL ROCKS OF THE 
KEWEENAW SERIES. 
To any one who will read through the foregoing part of this chapter 
it will become evident that between the several kinds of original rocks 
described there are no sharp lines, and that there is, in fact, a continuous 
series of kinds, from the most basic to the most acid. It will also become 
evident that, from the necessity of following some accepted nomenclature, 
it has been unavoidable to use names which cover very different ranges of 
acidity. In the following table an attempt is made to classify the various 
rocks with reference to silica content, as well as to texture and mineralogical 
composition, and thus to bring out more plainly than has been done in the 
preceding pages the relations of the different kinds to one another. The 
references B 1, A 1, &c., are to the several classes of basic and acid rocks, 
respectively, as given on pages 37 and 91. 
