122 NEW YORK STATE MUSEUM 



Its age relatiion is consistent also, as it seems to be the oldest of the 

 large igneous members. A more pronounced development is of 

 granitic character, such as the Canada Hill type. It is not 

 at all clear, however, where the line should be drawn between 

 the igneous representatives of this more ancient period and those of 

 a later time. But taking the suggestion that these older ones are 

 habitually more intimately intermixed with the Grenville so that 

 they tend to form a series with close gradations and transitions, 

 all of which also tend more strongly than do any of the others to 

 exhibit a true gneissic structure, we believe that this member is 

 represented in the West Point area also. Probably the Canada Hill 

 type of this report is the chief representative (see the petrographic 

 description). 



c The principal igneous invasion — the Algoman 



Represented in the Adirondack region by great intrusive masses of 

 gabbro, granite, anorthosite and syenite. Of these, it appears that 

 the gabbro is the earliest and the syenite the latest; but it does not 

 appear that any great d\namic revolution or any marked historical 

 hiatus separates them. The time represented is no doubt very long, 

 but normal geologic evidences are largely lacking except for the 

 fact that these igneous units cut each other and have a determinable 

 succession. Some of the members of this division exhibit rather 

 clear-cut and readily distinguished relations to the older series and 

 even their minor injection phenomena tend to develop more striking 

 lit-par-lit bands than were developed by the earlier invasions. They 

 also are said to involve xenolithic masses of the older rocks in great 

 profusion, but have not as a rule succeeded in destroying their iden- 

 tity or the evidences of their former character. 



Perhaps the crux of the whole correlation problem, as far at least 

 as it applies to the Adirondacks, is the possible identification of the 

 members of this division in the West Point area. The most striking 

 member, the anorthosite, is certainly not re])rcscnted, and this is 

 true also of the gabbro. But it is probable that the granite and the 

 syenite or their close equivalents arc represented by the Reservoir 

 and Mahopac granite on one hand and by the Storm King granite, as 

 the suggested equivalent of the Adirondacks syenite, on the other. 



The Adirondacks syenite is the greatest of the field units of that 

 region, showing much dififerentiation whose extent and behavior 

 suggest a great bathylithic source and probability of much greater 

 subsurface extent. It is the one member of this division, therefore, 



