334 THE JOURNAL OF GEOLOGY. 



subjected in pre-Cambrian times, and thus frequently taking 

 a line of least resistance and having been intruded between the 

 bands or strata of the Grenville series, have had a foliation 

 induced in them parallel to that of the gneiss, while in other 

 cases where they are more or less massive, they cut across the 

 the strike of the latter. 



In many cases the anorthosites which exhibit a perfect folia- 

 tion may be traced step by step into the massive variety, the 

 gradual development of a foliated structure in the rock being 

 accompanied by a progressive granulation of the constituents, 

 most beautifully seen under the microscope. The change, how- 

 ever, differs from any hitherto described in that it is purely 

 mechanical. There are no lines of shearing with accompanying 

 chemical changes, but a breaking up of the constituents through- 

 out the whole mass, though in some places this has progressed 

 much further than in others, unaccompanied by any alteration of 

 augite or hypersthene to hornblende, or of plagioclaseto saussurite, 

 these minerals, though prone to such alteration under pressure 

 remaining quite unaltered, suffering merely a granulation with 

 the arrangement of the granulated material in parallel strings. 

 This process can be observed in all its stages, and there is reason 

 to believe that it has been brought about by pressure acting on 

 the rocks when they were deeply buried and ver}' hot.' The 

 anorthosite areas, of which there are about a dozen of great 

 extent with many of smaller size, are distributed along the south 

 and southeastern edge of the main Archean Protaxis from Lab- 

 rador to Lake Champlain, occupying in this way a position 

 similar to that of volcanoes along the edge of our present conti- 

 nents. Curiously enough precisely similar occurrences of this 

 anorthosite have been found in connection with similar gneissic 

 rocks, supposed to be of Archean age, in Russia, Norway and 

 Egypt. These anorthosite rocks being intrusive, may be left out 

 of consideration in endeavoring to work out the succession of 

 the Archean in this great area. 



^ See Frank D. Adams — " Ueber das Norian oder Ober-Latirentian von Canada,^'' 

 Neiies Jahrbiich fiir Mineralogie, etc., Beilageband VIII., i8qs- 



