14 NEW YORK STATE MUSEUM 



The term " Syenite- Grenville complex" is used by the writer 

 because the rocks, for the most part at least, appear to be a rather 

 intricate mixture of the syenitic and Grenville rocks already de- 

 scribed. Especially in certain of the large exposures, as in the 

 vicinity of Forestport, Myers hill, north of Enos, near the northern 

 limit of the map along the railroad, etc., rocks which if present alone 

 would undoubtedly be classed with the syenite are closely associ- 

 ated with others which show characteristic features of the Gren- 

 ville. The two rocks show great variation in amount although 

 the syenites generally predominate. In large exposures in the 

 field the rocks of the complex may be easily distinguished from the 

 typical Grenville because the bands are not so well developed and 

 straight, and also because of the basic inclusions. They differ from 

 the pure syenite because of a better development of the gneissic 

 structure and a decided lack of homogeneity. 



There is strong evidence that the Grenville sediments are the 

 older and that the syenite has been intruded into them. One 

 argument ifi favor of this view is the fact that the two rocks are so 

 thoroughly involved and that neither may be said to rest upon the 

 other. But the strongest argument lies in the fact that portions 

 of the rocks mapped as Grenville may be seen as actual inclusions 

 within the syenite. Among the localities where such inclusions 

 occur are: at the bridge near the mouth of Little Black creek; 

 2 miles east of Enos on the south side of Ash ridge ; near Forestport ; 

 where the railroad crosses Big Woodhull creek; and to the south 

 of Myers hill. Thus the syenite appears to be intrusive into and 

 therefore younger than the Grenville. Certain results obtained b}'' 

 C. H. Smyth jr^ in the western Adirondacks seem to point to the 

 same conclusion. 



Because of the great variety of rocks mapped under this heading 

 and the frequent gradations of the different types into each other 

 it is very difficult clearly to describe them. In general it ma}^ be 

 said that nearly all of the minerals occurring in either the Gren- 

 ville or the syenite have been found in this complex and also that 

 the microperthite is lacking while the anorthoclase, plagioclase 

 and quartz as well as the dark colored minerals show all sorts of 

 variations in relative abundance. 



The most common type is a rock of syenitic character, which 

 in the hand specimen very closely resembles the homogeneous 

 syenite already described. Although under the microscope the 

 rock shows a general lack of microperthite and a greater richness 



1 N. Y. State Mus. 51st An. Rep't, v. 2. 1899. 



