l8 NEW YORK STATE MUSEUM 



Crystal outlines are sometimes distinct. Professor Kemp has noted 

 a similar pyroxene in the syenite of the Elizabethtown-Port Henry 

 quadrangles and he suggests the presence of the jadeite molecule 

 in its composition. Garnets seldom occur in this syenite. 



The most basic rock of all is shown by no. i of the table. This 

 rock makes up the Bull Rock mountain mass. It is unusually high 

 in plagioclase, pyroxene, and biotite and low in quartz, and is nearer 

 the gabbro in appearance and composition than any other rock of 

 the whole region. It is fine to medium grained and of rather a 

 bluish gray than greenish gray color when fresh. 



Numbers 2 and 3 of the table are from the mountain 2 miles 

 south-southeast of Riverside, and from along the road i mile west- 

 southwest of Daggett pond respectively. In the field it is generally 

 impossible to distinguish this pyroxene syenite from much of the 

 granitic hornblende syenite and this, together with the fact that the 

 two rocks grade perfectly into each. other, renders separate map- 

 ping practically impossible. The pyroxene syenite, however, is 

 certainly less common than the hornblende syenite. 



Granitic hornblende syenite. The range in mineral composition 

 of this rock is shown by the selected examples given in table i. 

 Microperthite and orthoclase are always present though in very 

 variable amounts, while the quartz and hornblende contents are 

 high and biotite is scarcely represented. In addition to the minerals 

 shown in the table a few scattering garnets sometimes occur. No. 

 7, with its almost total lack of hornblende, is an unusual type. 

 The gneissic structure is usually well developed though at times 

 it becomes very faint. This granitic syenite on the one hand grades 

 perfectly into the pyroxene syenite and on the other into the gran- 

 ites below described. Arbitrarily, when the quartz content passes 

 beyond 25 per cent, the rock is classed as granite and, as nearly 

 as possible, the rocks have been separately mapped on this basis. 

 The very common presence of biotite in the granite has also been 

 a help in mapping. 



Numbers 4, 5, 6, and 7 are respectively from Potter mountain, 

 I j/4 miles east of Pottersville, one-third of a mile north of the north 

 end of Loon lake, and the summit of Little mountain. 



GRANITE 



As already stated, the granitic syenite passes through perfect 

 gradations into the granite and these rocks are very clearly only 

 different phases of the same great intrusive body. The rock is 

 rather arbitrarily called granite when it contains more than 25 



