46 NEW YORK STATE MUSEUM 



between the syenite and anorthosite. The conclusion, therefore, 

 based upon the field relations and composition of the rocks is that 

 we have here a true magmatic assimilation product, the invading 

 syenite magma having actually incorporated and assimilated more 

 or less of the anorthosite material. The close juxtaposition of sye- 

 nite and Keene gneiss may be reasonably explained if we consider 

 the syenite to have been an intrusion as an off-shoot of the great 

 body of syenite magma into previously formed and cooling (or 

 possibly solidified) Keene gneiss magma, the temperature then 

 having been high enough only to permit fusion along a narrow 

 border zone between the intruded and intrusive masses, thus 

 accounting for the narrow transition zone between the two in the 

 ledge. The foliation of the Keene gneiss is quite certainly an orig- 

 inal structure due to magmatic flowage under pressure, and accord- 

 ingly the marked differences in degree of foliation within this one 

 outcrop are regarded as the result of differential magmatic flowage 

 according to the principles explained beyond under the caption' 

 " Foliation." 



Professor Kemp has informed the writer that rock similar to 

 that just described was formerly visible in outcrop at the present 

 sawmill site in Keene village, and the area of Keene gneiss is 

 accordingly extended that far south on the geologic map. 



The little area one-half of a mile east of Keene shows a variable 

 lot of rocks, some being apparently Whiteface anorthosite, some 

 rich in black minerals and garnet, and much containing large bluish 

 gray labradorites in a very syenitic looking, crudely gneissoid, 

 brownish-weathered rock like the typical Keene gneiss above 

 described except for its brown weathering. 



Oak ridge shows fine big exposures of a rock which, in the field, 

 would be taken for a rather basic phase of syenite except for the 

 large scattering bluish gray labradorites. It is, without doubt, a 

 large scale mass of the Keene gneiss. 



Good outcrops of typical Keene gneiss also occur in the small 

 areas respectively i mile northeast ; 2 miles west-northwest ; and 

 4^ miles west of the village of Keene. 



Areas near Upper Jay. In the area of over one-half of a square 

 mile just east of Upper Jay, there are many very good exposures, 

 certain of them of particular interest because they throw important 

 light upon the origin and relations of the Keene gneiss. Near the 

 top of the hill at the northeastern border of the area, Whiteface 

 anorthosite and syenite in big exposures are separated by a zone, 

 a few feet wide, of basic syenitelike rock with scattering bluish 



