GEOLOGY OF THE LUZERNE QUADRANGLE I7 



classed with the gabbro and metagabbro which in some cases have 

 been affected by the granite intrusions. 



The possibility that the amphibolites may be in part at least highly 

 metamorphosed portions of the Grenville series should not be over- 

 looked. Thus Adams,® in his description of the amphibolites of the 

 Glamorgan granite of Ontario, Canada, says : " The limestone 

 (Grenville), toward the granite contact, passes gradually over into 

 amphibolite, the latter being undoubtedly produced by the action of 

 the former." Not only is positive evidence for any such action 

 lacking within the quadrangle, but also, in the North Creek quad- 

 rangle just to the north, limestone masses directly associated with 

 syenite and granite show no signs of change to amphibolite. In the 

 writer's experience in the Adirondacks in general, and in the 

 Luzerne and North Creek quadrangles in particular, those amphibo- 

 lites or hornblende gneisses which are quite certainly interbedded 

 with the Grenville series are commonly garnetiferous and usually 

 interstratified with other materials of rather definitely sedimentary 

 origin. 



Gushing,' in his report on the Ogdensburg quadrangle, thinks it 

 most likely that the amphibolites there are in part metamorphosed 

 Grenville strata, and in part metagabbro. Martin,^ who has care- 

 fully considered the amphibolites of the Canton quadrangle, 

 strongly inclines to the view that most or all the amphibolites there 

 represent metagabbro intermediate in age between the Grenville and 

 granite. The writer has been led to a similar conclusion in his 

 studies of the Lyon Mountain and Russell quadrangles. All things 

 considered, then, and recognizing the uncertainties regarding the 

 problem of the origin of some of the amphibolites of the Luzerne 

 quadrangle, the writer believes the best evidence indicates that most 

 or all of them were derived from rather basic igneous rocks, prob- 

 ably chiefly or wholly gabbro. 



Sixty-three areas of gabbro and amphibolites are represented on 

 the accompanying geologic map, and many more similar bodies of 

 gabbro must occur mostly concealed under Pleistocene deposits. 

 Many strips or lenses too small to be mapped were also observed. 

 Also in many of the areas of mixed rocks, gabbro and amphibolite 

 are prominently developed, but these are generally too involved 

 with other rocks to make separate mapping possible. 



•Jour. Geol., 17, 1909, p. 8. 



^N. Y. State Mus. Bui. 191, 1916, p. 14-16. 



'N. Y. State Mus. Bui. 185, 1916, p. 50-65. 



