PETEOGEAPHY OF ONTAEIO. 47 



IV. — Massive and Schistose Rocks. 



In the treatment of these rocks, the line between massive and schistose cannot be 

 drawn so closely as in the study of rocks in situ, where the broad structural lines are 

 easily seen. Eocks which, on the small scale of a boulder, shew no trace of parallelism 

 in their constituents, will be considered " massive " ; but in the case of the granites and 

 gneisses, where most of the difficulty occurs, the distinction is perhaps not vital ; since, 

 in many places, as, for instance, in the Thousand Islands, the two seem to run into one 

 another. 



In general, for the massive rocks, the arrangement of Rosenbusch' will be followed, 

 while, for the schistose rocks von Lasaulx" will be taken as guide. 



These rocks maybe divided broadly into an acid and a basic series, and we shall com- 

 mence with the acid series, which is characterised by the presence of one or more species 

 of potassium felspar. It may be subdivided into a subseries containing quartz as an 

 essential mineral, and a subseries devoid of quartz, or nearly so. 



ACID SERIES. 

 A. 

 MASSIVE. 

 (1.) Those conlaiiiiiig <tiiar(z. 



The Granites. 



The admirable description of the granites and their constituent minerals given by 

 Rosenbusch^ holds for the most part when applied to'the granites of the drift of Ontario, 

 though one exception should be made in the case of orthoclase, which Rosenbusch makes 

 an essential element, while in some of our granites it is almost wholly replaced by a 

 triclinic orthoclase felspar, microcline. 



We shall define granite as " a rock composed chiefly of quartz, orthoclase or 

 microcline, and some sodium-calcium-felspar, with more or less biotite, muscovite or 

 hornblende." Taking up the minerals in this order, we have : — 



Quartz. — This never shews crystalline faces, so far as my observations go, but always 

 forms irregular masses and fragments, consisting, as shewn by polarised light, sometimes 

 of but one individual, sometimes of a number clustered together. It is always fresh and 

 transparent, unless rendered turbid by cavities and inclusions, which are often very 

 numerous. The cavities may contain a liquid (water or carbonic acid), a moving bubble, 

 and often also a cube of salt. Solid inclusions of various kinds also occur, slender and 

 hair-like, or interrupted like telegraphic characters, or cut iip into rows of dots, or scat- 

 tered as dusty particles. Hexagonal plates of a drab color, partly covered with red oxide 



' Mikroskopische Physiographie der massigen Gesteine, 1878. 



- Einfuhrung in die Gesteinslehre, 1886. » Mikros. Phys. der mas. Gest., pp. 7, etc. 



