BDPORT OF THE DIRECTOR AND STATE GEOLOGIST 1900 r57 



and which is therefore later^ biut at the same time would seem to 

 represent an important member of the eruptive series that makes 

 up the heart of the Adirondacks. As one recedes £rom the main 

 syenite mass, the syenite content of the border zone becomes con- 

 tinually smaller and eventually disappears, while the granitic 

 gneiss spreads away to the south and west. But even well away 

 from the main syenite mass, email bodies of syenite are fre- 

 quently met which are seldom accommodating enough to disclose 

 their relationships to the surrounding granite. Patches of the 

 Orenville rocks, or of doubtful gneisees w^hich are likely of Gren- 

 ville affiliations, are found here and there, but such patches occur 

 also in the midst of the syenites and anorthosites. This border 

 zone differs slightly from that on the north, and the evidence 

 that we are dealing with a mixed belt of syenite and granite 

 lying betw^een a syenite mass and a granite mass, seems stronger 

 than on the north, though it appears to be also the case there, 

 the rocks' just about Piercefield being of somewhat doubtful 

 association. 



GENERAL CONCLiUSIONS 



The above recorded observations seem to the writer to prove in 

 some cases, and to strongly indicate in others: 



1 that the Adirondack anorthosite is cut intrusively by an 

 augite syenite which is therefore younger; 



2 that, w hile the larger part of the augite syenite of the Adiron- 

 dacks is in such situation with respect to the anorthosite as to 

 render impossible any determinations of relative age, its general 

 character is so uniform throughout that it is exceedingly probable 

 that it is all of the same approximate age and consists of intru- 

 sions from the same source; 



3 that at their borders these syenites pass over into granites, 

 part of which at least cut the syenite eruptively and are there- 

 fore younger; 



4 that the syenite grades into granite on the one hand and into 

 gabbro diorite on the other, and apparently into anorthosite as 

 well : 



