KELATlUXSlllP TO THE ANOKTHOblTKb 1 8U 



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 anorthositc 

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

 and there is some question of its identit3^ 



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 wh}^ differentiation should not have taken place for 

 the most part ])efore the intrusion of either, and yet that a fux^ther 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. 



SiMlLAK PeTROGRAPHIC PROVINCES 

 (UNA DA NORTH OF 3WN TUBAL 



The rocks of the Adirondacks are most naturally compared with those 

 of Canada to the north, being separated from them by a comparatively 

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

 continuous. That rocks corresponding to these syenite-gneisses are 

 present there is undoubted, though as 3"et no attempt has been made to 

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

 prising, considering the difficulty 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 strongly 

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

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

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

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

 many varieties represented approaching 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 anortliosite. 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. 1). Adams : GeoL Surv. Can., Ann. Rep., \ol. vui, 1S9C, pt, J, p. 121 



