186 THE CANADIAN NATURALIST. [June, 



many other places to the northeast, and along the frontier of Can- 

 ada. It is worthy of note, that the intrusive masses on the two 

 iides of the mountain range are, so far as yet observed, entirely 

 distinct in character; and that er 'ptive rocks are generally want- 

 ing among the Notre Dame Mountains, which consist chiefly of 

 stratified rocks. It is also to be remarked, that the intrusive gra- 

 nites at their eastern base, are not unlike, in mineralogical charac- 

 ters, to the indisjenous srranites of the mountains ; thus sua;2;est- 

 ing he view that these are possibly the source of the intrusive 

 granites which break through the I 'evonian strata. A similar 

 relation has been pointed out by Durocher, in Scandin ivia, where 

 the palaeozoic strata are broken by intrusive masses of granite, 

 Orthophyre, zircon-syenite, and diorite. These rocks, according to 

 him, are specifically analogous to those of the underlying primitive 

 gniess. but petro2;raphically distinct. (Bull. Soc. GJol. de Fr nee, 

 [2], vi 33.) These facts are in accordance with the theory of 

 eruptive roeVs developed at the commencement oP this paper ; and 

 it would be easy to extend the comparison to the intrusive diorites 

 and dolorites abo it Montreal, and to show their resemblance with 

 the stratified feldspithic rocks of tha Labrador series. (Silli- 

 nian's Journal [2], xxix, 283, and xxxi, 414.) 



IV. Local Metamorphism. 



In the second part of this paper I have asserted that the silicated 

 minerals of crystalline rocks have a two-fold origin. In the first 

 place they may result from the molecular change of silicated sedi- 

 ments. These ar ' either derived from the mechanical disinteo;ration 

 and pirti il decomposition of pre-existing silicates, or have been gen- 

 erated by chemical processes in waters at the earth's surface. In 

 this way steatite, serpentine, pyroxene, hornblende, chlorite, and in 

 many cases gar et, epidote, and other silicates, are formed by a 

 crystallization and molecular re-arrangement of chemically form d 

 silicates, in a manner analogous to that in which mechanically de- 

 rived clays are converted into crystalline species. I have however 

 pointed out that in the second place many of tiiese silicated minerals 

 may bj generated by chemical reactions which take place among the 

 mechanically mixed elements of sediments under the influence of heat 

 aided by alkaline solutions. Both of these methods are involved in 

 rock-nietamor[)hism ; and in the case of the local alteration of ocks 

 by igneoas masses, it is easy by comparative examinations to trace 



