20 NEW YORK STATE MUSEUM 



crude banded effect. Some pegmatites cut across the foliation. 

 Toward the north the gabbro is massive and scarcely foliated. 



In the area i^ miles southeast of Gailey hill the gabbro, which 

 varies to amphibolite, is cut by a good many pegmatite dikes some 

 of them carrying magnetite. 



On Mount Anthony the metagabbro is mostly amphibolite cut 

 parallel to its foliation by many small granite or grano-syenite dikes 

 and some pegmatites. 



At the sharp turn of the river road one-half of a mile west of the 

 top of Jeffers mountain there is an instructive exposure of gabbro 

 freshly opened up by blasting. Most of the rock is medium grained, 

 fairly ophitic and nonfoliated. A thin section contains labradorite, 

 50 per cent; hypersthene, 22 per cent; diallage, 14 per cent; horn- 

 blende, 10 per cent; biotite, 2 per cent; and a little magnetite and 

 pyrite. On its east side some of the gabbro is more or less foliated 

 and injected with granite, and some is simply fine grained and dis- 

 tinctly foliated. In this involved metagabbro there are some 

 garnets. 



The mass of metagabbro three-fourths of a mile north of Hunt 

 lake is well foliated amphibolite cut irregularly by some highly 

 foliated dikes of coarse granite. 



Syenite-granite Series 



General considerations. As is well known, the syenite-granite 

 series is widespread and abundantly developed throughout the Adi- 

 rondack region. In the Luzerne quadrangle the members of this 

 series, especially the granite, are by far the most extensive of all 

 the rocks. These rocks show many variations from medium- 

 grained quartz syenite through grano-syenite to granite and 

 through monzonite to quartz diorite. Satellitic dikes of pegmatite, 

 silexite and aplite are common. In view of the fact that Professor 

 Gushing has advocated^ the existence of two very distinct ages of 

 granite in the Adirondacks, the writer was constantly on the look- 

 out for evidence of this kind. In spite of diligent search the writer 

 was, however, unable to find anything like convincing evidence for 

 two granites of really different geologic ages. All observed phe- 

 nomena may be satisfactorily explained on the basis of a single 

 great syenite-granite series, evidence for which is presented beyond 

 in the more detailed descriptions. This does not, of course, mean 

 that all the facies of the syenite-granite series are exactly of the 



'Amer. Jour. Sci., v. 39, 1914, p. 2S8-94. 



