38 NEW YORK STATE MUSEUM 



while others are more sharply separated. There are also many 

 degrees of foliation and granulation, and differences in coarseness 

 of grain. 



The conception of the origin of such variations which best har- 

 monizes with the field facts may be briefly stated as follows . Dur- 

 ing the crystallization of the anorthosite magma, formed by the 

 process outlined above, there was local differentiation in the upper 

 portion of the magma reservoir whereby many portions relatively 

 richer in femic constituents separated from the much larger por- 

 tions relatively poor in femic constituents. The more femic por- 

 tions, which contained more liquid, and hence were freer to flow, 

 were, in many cases, more or less shifted by movements during a 

 late stage of magma consolidation to form the crude bands or zones 

 often well foliated and rather sharply separated from the purer 

 anorthosite. Those belts or zones of more gabbroid anorthosite 

 which gradually pass into purer anorthosite probably represent 

 differentiates- essentially in situ. That there must have been notable 

 movements during a late stage of magma consolidation is abun- 

 dantly proved by the magmatic flow-structure foliation, more 

 especially in the gabbroid zones, but also not rarely in the typical 

 Marcy anorthosite. It is also believed that these late magmatic 

 movements caused much, or all, of the notable granulation of the 

 anorthosite. But this granulation is by no means true only of the 

 anorthosite. The syenite-granite series and the later gabbro usu- 

 ally exhibit high degrees of granulation and more or less well- 

 developed foliation due to the same cause. 



Syenite-granite Series 



General statements. The syenite-granite series is very promi- 

 nently developed in the Schroon Lake quadrangle where it occu- 

 pies most of the southeastern half of the area. Definitely known 

 areas, essentially free from intimate associations with other rocks, 

 total fully 75 square miles. To these must be added a few square 

 miles more which are mapped with the mixed rocks or are con- 

 cealed in the areas mapped as Pleistocene. The syenite-granite 

 series is, therefore, about as extensively developed as the anortho- 

 site series of the quadrangle. No syenite or granite whatever was 

 found in the great area of Marcy anorthosite, and an explanation of 

 this fact is offered above in the discussion of the anorthosite. The 



