B. A. Daly — Mechanics of Igneous Intrusion. 41 



mature consideration this suggestion seems inadequate and a 

 more general explanation must be sought. 



Adams describes the great anorthosite mass of Morin, Que- 

 bec, as genetically associated with an adjacent gabbro body of 

 batholithic size." The one is either a differentiate from the 

 other or both are expressions of a common basic magma. The 

 latter seems the more probable relation. In fact, both batho- 

 liths appear to represent the crystallized products of a magma 

 allied to, if not identical with, the primary basaltic magma 

 which has been the source of the heat in post-Archean batho- 

 lithic intrusions. 



The conditions of intrusion for these "upper Laurentian " 

 masses seem to have differed from those typically represented 

 in the post-Cambrian batholiths. The latter have been devel- 

 oped under heavy geosynclinal covers which have entailed 

 considerable superheat in the basaltic substratum. It is not 

 impossible that the "upper Laurentian" basic magmas, already 

 cooled nearly to the solidification -point, were injected into the 

 then thinner crust, or warped up with it, during crustal dis- 

 turbance. Lacking superheat these magmas lacked stoping and 

 assimilating power and, consequently, did not become acidified. 



In favor of the conception that these magmas were near 

 the solidification point at the time uf their intrusion, is the 

 fact that the anorthosites often show primary banding and are 

 most extraordinarily granulated, as if by dynamic force which 

 acted on the congealing mass near the close of the intrusion- 

 period. Concerning the granulation Adams writes : "There 

 are no lines of shearing with accompanying chemical changes, 

 but a breaking up of the constituents throughout 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 plagioclase to 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 rocks when they were deeply buried and very 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 Labrador to Lake Champlain, occupying in this way a 

 position similar to that of volcanoes along the edge of our 

 present continent. " f 



* Canadian Record, of Science, 1894-5. 



fF. D. Adams, Jour, of Geol., i, p. 334, 1893. 



