520 J. A. DRESSER, IGNEOUS ROCKS OE EASTERN QUEBEC 



relations can be satisfactorily discussed; yet certain general relations 

 may now be deduced, and these conclusions, it is hoped, may be amplified 

 and more precisely applied at some later time, when all the rocks in ques- 

 tion have become better known. 



In general terms it may be said that those rocks of a definite district 

 belong to the same province,* whose phases in their nearest approach to 

 one another do not differ more widely than the various differentiates of 

 any single mass. Thus the porphyry-andesite series differs in its acid 

 phase from the granites, as far as the latter are known, chiefly in degree of 

 crystallization, not in composition. The more basic phase of the old 

 volcanics, as has been shown, passes into a rock which has altered into 

 serpentine by differentiation in situ. Hence this oldest group seems to 

 form a connecting link between the granites on one hand and the diabase 

 serpentines, etcetera, on the other, while the hornblende granites similarly 

 connect the diabases and normal granites. Accordingly, those three 

 groups form part of a single petrographic province, according to the 

 definitions quoted above ; but the Monteregian rocks appear more distinct 

 throughout the quite extensive range of variation within themselves. The 

 individual hills differ from one another in a comparatively small degree ; 

 also their distinctive characteristics are not found in any measure in the 

 other groups of rocks mentioned. Should a detailed study of the granites 

 show that within them are differentiated portions of more basic rocks — 

 for example, should nepheline syenite be found in association with them, 

 as it has been found in some cases in the Hastings district by Doctors 

 Adams and Barlow, f they would then appear as an acid extreme toward 

 the east of the Monteregian series. But this has not been done, nor is 

 there at present any valid reason for expecting such phenomena to be 

 found. While the Monteregians appear at regular intervals at upward of 

 10 miles across the plain, no rocks of a consanguineous type have been 

 found to the east of Shefford mountain, although a careful examination 

 has been made in that direction throughout the district wherever igneous 

 rocks are known to occur. In the later dikes an indication of rocks of 

 the Monteregian type exists; for while it is conceivable that almost any 

 rock might be differentiated in small amounts from almost any magma, 

 it is the most common relationship to find camptonite and bostonite types 

 differentiated from highly alkaline magma such as that of the Montere- 

 gian rocks; but the wide distribution of these dikes and their relatively 

 small amount make them less important factors in considering the limits 



* Dr H. S. Washington : "Petrographic province of Essex county, Massachusetts." 

 Journal of Geology, vols, vi and vil. 



t Summary Report, Geological Survey of Canada, 1898. 



