318 NEW YORK STATE MUSEUM 



as to (ho age relations as are the Diana exposures, but which, 

 nevertheless presents some interesting features, as indicated by 

 the accompanying section [fig. 2]. The augite syenite constitutes 

 the center and south end of the section. It is more thoroughly 

 granular and gneissoid than in the neighboring exposures. Sep- 

 arating the two syenite areas is a mass of banded .gneiss 12 feet 

 in thickness [pi. 3]. Above is a 2 foot layer of a white, gran- 

 ular rock composed of quartz and white pyroxene in the propor- 

 tion of 1 to 2. This is followed by layers of black pyroxene 

 granulite and light colored quartzose rocks, the latter consist un- 

 essentially of quartz and alkali feldspars in the proportions of 2 

 to 1. The structure and composition indicate the sedimentary 

 origin, and identical gneisses are found elsewhere in intimate 

 association with limestones. The section is cut at but a small 

 angle with the strike, and but one of the contacts is exposed. 



A ob A 



Fig. 2 Section in railroad cut near Loon lake, N. Y. A, augite-syenite. B, well 

 banded quartzose gneisses. (7, quartzose gneisses. J), biotitic sheared strip — strike 

 north 10 degrees west. Dip of bedding and foliation 65 degrees to the west. 



This is parallel to the foliation and bedding and appears like a 

 shear zone, marked by abundant development of biotite. Beyond 

 this middle mass of syenite fine grained, red, granitic gneisses 

 come in, which are likely igneous but quite like rocks often closely 

 associated with the Grenville. The contacts of this rock with the 

 syenite are not exposed. All the rocks have a common foliation, 

 which is also parallel to the banding of the banded gneiss. 



While the field relations are not well shown, the fact that the 

 syenite extends unbroken for some distance on all sides of the 

 exposure, and that no Grenville rocks are elsewhere exposed, 

 makes it evident that we are dealing with but a small mass of 

 these rocks wholly surrounded by syenite and hence of the nature 

 of an inclosure in it. Many examples of precisely similar nature 

 may be cited from the areas occupied by the great intrusions. 



Relations of syenite and anorthosite. Just as the Diama syenite 

 belt, because of juxtaposition to a considerable area of the Gren- 

 ville rocks, has furnished conclusive proofs of the age relations 



