ELIZAr,ETHTOWN AND PORT HENRY QUADRANGLES 8l 



been done by Professor Gushing in the Long Lake sheet, and sub- 

 mit in the text the details of such intrusive relations as had been 

 detected. 



Again, if we start with the typical syenites of which there are 

 good representatives, we find variations both toward the acidic and 

 the basic extremes. Full details with analyses of these are given in 

 the pages discussing the syenite series and under the ore bodies of 

 Mineville, where the diamond drill has afforded exceptional facil- 

 ities for study. The basic phases when sheared into gneisses afford 

 rocks almost if not quite indistinguishable to the eye, from the basic 

 phases of the anorthosites. Thin sections can not be prepared nor 

 can microscopic determinations be made of every exposure. In- 

 deed their importance and help can be easily overrated. Much un- 

 certainty has been unavoidably felt. The writer can only state 

 that after repeated study, he has chosen the coloring to the best of 

 his ability. The acidic extreme on the other hand approaches 

 both the granitic series and the possibilities of metamorphosed 

 sediments. 



Finally the basic gabbros have not escaped the general shearing 

 and visibly pass into gneissoid phases in excellent exposures. They 

 imitate almost if not quite indistinguishably basic phases of both 

 syenites and anorthosites and contribute to the difficulties not alone 

 of drawing boundaries, but of identification itself. Starting out 

 from a typical and easily recognized exposure of massive gabbros, 

 one may pass over dark gneisses, and hybrid types almost without 

 limit, before another sharply identifiable ledge is met. 



The lack of sharpness of characters has led the writer to look 

 somewhat favorably upon the possibilities of infusion among the 

 deep seated rocks. That is, a great plutonic mass may have ab- 

 sorbed into its border portions of so much of the older wall rock as 

 to give an intermediate result neither one thing nor the other. While 

 perhaps a difficult process to demonstrate, it nevertheless has its 

 attractions and its reasonable side. If, for instance, anorthosites 

 grow more basic at the borders, and if we have only fragments of 

 an old limestone bearing Grenville series left, like islands at times 

 in its midst, what more natural than that by absorption the bases of 

 the old anorthosite magma have been increased to the point where 

 pyroxenes and hornblendes become inevitable. An original magma, 

 heated well above the bare requirements of fusion would, of course, 

 be necessary to bring about this process, but there seems no insuper- 

 able objection to it at the heart of a great igneous center. 



