RELATIONSHIP TO THE ANOKTHOSITES 180 



approach toward the syenite, but no strictly intermediate varieties are 

 yet forthcoming. 



In other places the passage from one rock to the other is quite abrupt, 

 with no sign of blending. Unfortunatel}' no contacts have been noted, 

 so that there is nothing to show which rock is the older. In two or three 

 instances what seem to be small inclosures of unmistakable anorthosite 

 in the syenite have been noted, but in each the latter is far from fresh, 

 and there is some question of its identit}'. 



The fact that areas of each are found wholl}^ apart from any trace of 

 the other is good evidence for the separate nature of the intrusions ; nor 

 is there any reason why differentiation should not have taken place for 

 tlie most part before the intrusion of either, and yet that a further differ- 

 entiation of local character should not also take place in parts of the 

 anorthosite after reaching their present resting place and while yet un- 

 cooled. 



Similar Petrographic Provinces 



canada north of montreal 



The rocks of the Adirondacks are most naturally compared with those 

 of Canada to the north, being sei)arated from them b}^ a comparatively 

 narrow belt of Paleozoic rocks, beneath which the two are undoubtedly 

 continuous. Tliat rocks corresponding to these sj^enite-gneisses are 

 present there is undoubted, tliough as 3'et no attempt has been made to 

 differentiate them from the other gneisses of the region. This is not sur- 

 l^rising, considering the difficult}^ of the task and the nature of the country 

 to be explored. 



Adams has described the Saint Jerome anorthosite as 



"Surrounded by a zone of rocks of varied character, many of which sti'ongly 

 resemble the anorthosite in appearance, but are quite different in composition," 

 and which " consists chiefly of rocks whicb, in addition to augite and plagioclase, 

 contain variable amounts of hornblende, ortlioclase, and quartz, and which are 

 thus intermediate in character between the gneiss and the anorthosite, some of the 

 many varieties represented appi-oaching more nearly to gneiss and others more 

 nearly to anorthosite in character and composition." * 



He expresses the opinion also that the zone is to be regarded as a 

 peculiar border facies of the anorthosite. If this be the true explanation 

 and the writer is correct in his correlation, the area furnishes evidence of 

 the passage of one rock into the other of much more decisive character 

 than any yet forthcoming in the Adirondacks. 



* F. D. Adams : Geol. Surv. Can., Ann. Rep., vol. viii, 189G, i^t. J, p. 121. 



