742 A TREATISE ON METAMORPRISM. 



the massive igneous rocks, and especially the plutonic rocks, which contain 

 little combined water, and when deformed are apt to be granulated rather 

 than recrystallized. One of the best districts to illustrate the principle is 

 the Original Laurentian area described by Adams." In this district are the 

 anorthosites, the Grenville sedimentary series, and the Basement gneiss of 

 igneous origin. Adams's careful descriptions show that the most funda- 

 mental point of difference between the three classes of rocks in their response 

 to deformation is in reference to recrystallization and granulation. The 

 sedimentary rocks of the Grenville series have been completely recrystal- 

 lized and are typical schists.'' The igneous gneisses are largely deformed 

 by granulation, but "the granulation has perhaps been effected, in part at 

 least, by recrystallization." " The anorthosites have been almost wholly 

 deformed by granulation/ Corresponding exactly with these facts are the 

 amounts of contained water. Analyses of three recrystallized Grenville 

 gneisses give an average water content of 1.46 per cent. 8 An analysis of 

 one partly granulated and partly recrystallized gneiss of igneous origin 

 gives 0.70 per cent of water/ An analysis of granulated anorthosites gives 

 only 0.51 per cent of water/ 



The frequent granulation of the massive igneous rocks does not con- 

 tradict the conclusion (pp. 712-713) that in many cases water as a source of 

 recrystallization may be derived from the plutonic rocks during- recrystalli- 

 zation. The very fact that water is given off during this process leaves the 

 plutonic rocks deficient in combined water. When later mass movements 

 take place with only a very small amount of combined water present, 

 granulation is likely to occur, and, as already noted, somewhat in pro- 

 portion to the amount of the residual water; for, as shown by the illustra- 

 tions already given, the anorthosites, containing a small amount of water, 

 under mass movement have been granulated to a greater extent than the 

 granites, which contain somewhat greater amounts of combined water. 



As examples of recrystallized schists of igneous origin may be men- 



« Adams, F. D., report on the geology of a portion of the Laurentian area lying to the north of 

 the Island of Montreal: Ann. Kept. Geol. Surv. Canada, vol. 8, 1895, pt. j, p. 1S4. 

 & Adams, cit., pp. 49-66. 

 « Adams, cit, p. 45. 

 a Adams, cit., p. 106. 

 « Adams, cit., p. 58. 

 /Adams, cit., p. 43. 

 v Adams, cit., p. 130. 



