GENETIC RELATIONS OF THE TGNEOUS ROCKS 521 



of the petrographic provinces. Thus, while camptonites and bostonites 

 may occur in many places to the east of the Sutton Mountain anticline 

 and diabase far to the west of it, as Drummondville or Saint Flavien, they 

 rather illustrate what Professor Pirsson * has recently called the progres- 

 sion of rock types than the extension of the boundary of either of the two 

 distinct groups of rocks mentioned. It would therefore seem that the 

 rocks of the Monteregian hills differ from the other rocks described in 

 this article more widely than any of those from one another — that is, 

 that the difference is a generic rather than a specific one ; hence the rela- 

 tion could be best defined as that of two contiguous provinces rather than 

 as parts of one province, even in the larger sense. 



The study of the consanguinity of rocks tends toward the hypothesis 

 that the interior of the earth may be regarded as containing a single 

 magma of uniform character which by process of differentiation within 

 the crust of the earth, or during the process of extrusion, or during the 

 process of cooling after extrusion gives rise to all classes of igneous rock. 

 This is the extreme view of the origin of different species of igneous 

 rocks by the process of differentiation. Partly in opposition to this is 

 that known as the assimilation theory, which supposes igneous rocks to 

 owe many of their present differences to the older rocks with which they- 

 have come in contact and by which they have been modified. This 

 theory could scarcely receive, under any circumstances, such wide appli- 

 cation as that just assigned to the differentiation theory, namely, that all 

 rocks have come from a universal common magma and are differentiated 

 only by the rock material with which they come in contact; nor could it 

 be counted a directly essential character in large extrusive volcanic out- 

 puts ; but in consideration of intrusive rocks where the invading lava may 

 for long periods of time have been slowly taking in and dissolving the 

 surrounding rock material, the process of magmatic stoping-j- may have 

 made the assimilation factor an important one in the modification of 

 igneous rocks. 



The Monteregian hills are all intrusive and are comparatively small 

 igneous masses; they have penetrated strata of different mineralogical 

 and chemical composition. Thus the Hudson Eiver mudstones, Trenton 

 limestones, the graphitic limestone, and black slates of the Farnham and 

 Phillipsburg series, as well as the quartz mica-schists of the Sillery, have 

 been penetrated by these* rocks without producing any material change in 

 the rocks themselves beyond a generally well marked endomorphic con- 



* American Journal of Science, July, 1905. 



t Dr R. A. Daly : "On the mechanics of igneous intrusives," Am. Jour. Sci., 1903 ; 

 ibid., August, 1905. 



XLVII — Bull. Geol. Soc. Am., Vol. 17, 1905 



