258 THE CANADIAN NATURALIST. [Vol. ix. 



but rather to agencies at work in a cooling igneous mass. The 

 igneous origin of gneisses, petrosilex-porphyries, diorites, ser- 

 pentines, and even of magnetic and specular iron-ores was held 

 and taught almost universally by our geologists a generation 

 since, and has still its avowed partizans ; some maintaining that 

 these various crystalline rocks are portions of the first-formed 

 crust of the planet, while others imagine them to be volcanic 

 matters extravasated at more recent date ; in either case however, 

 more or less modified by supposed metasomatic processes. By 

 the term metasomatosis are conveniently designated those changes 

 which are not simply internal (diagenesis), but are effected from 

 without, — as a result of which the chemical elements of the 

 original rock are supposed to be either wholly or in part replaced 

 by others from external sources (epigeuesis). 



The other school, to which allusion has been made, and which, 

 not less than the preceding, has helped to discourage, in the 

 writer's opinion, the intelligent geognostical study of the crystal- 

 line stratiform rocks, is that which believes them to be, iu great 

 part at least, the result of chemical changes, often metasomatic 

 in their nature, which have been effected in paleozoic and more 

 recent sedimentary beds, obliterating their organic remains, and 

 transforming them into crystalline strata. According to this 

 view, feldspathic, hornblendic, and micaceous stratiform crystal- 

 line rocks having similar mineralogical and lithological characters, 

 may belong to widely separated geological periods, — while the 

 same geological series may, in one part of its distribution, consist 

 of uncrystalline silicious, calcareous, and argillaceous fossiliferous 

 sediments, and in another locality, not far remote, be found, as 

 the result of subsequent changes effected in these strata, trans- 

 formed into gneiss, hornblende-schist or mica-shist, by what is 

 vaguely designated as metamorphism. 



The recent history of geology abounds in striking illustrations 

 of the fact that in a great number of cases these viewn have been 

 based on misconceptions in stratigraphy, and without entering 

 into the discussion of the question, it may be said that, in the 

 writer's opinion, careful stratigraphical study will, in all cases, 

 suffice to show the error, both of the plutonic and the metamor- 

 phic hypotheses of the origin of crystalline rocks. The former 

 is supported chiefly by the lithological resemblances between 

 certain stratified and unstratified rocks, and by the appearances 

 of stratification occasionally found in these ; while the latter is 



