(il-:()lJ)(i\' ()!• SAKAIOCA SI'KI.\(;S AND XICIMTV 2/ 



Ifudsoii cuts through this mass, some quarrying lias been done in 

 it to furnish masonry for Si)iers dam, and hence the general ex- 

 hibit of the rock alcjng the river is the best to be found within the 

 (juadrangles. U]) the hill west of Corinth is the southern half to two- 

 thirds of another mass running north on to the Luzerne sheet ; and 

 the third area runs west from Lake Desolation and Mt Pleasant 

 and its western extension may be seen on the map of the Broadalbin 

 (juadrangle.' It should be clearly understood that the boundaries 

 between the syenite and the (Irenville, as drawn on the ma])S, are 

 of the most vague (lescri])tion. A multitude of dikes run out from 

 the syenite into the (irenville; the syenite is full of inclusions of 

 (Irenville and the whole combination has been much deformed. 

 There is plenty of syenite outside the areas mapped as such and 

 there is much (iren\ille within the areas mapped as syenite. The 

 best that can be done on maps of this scale is to endeavor to map 

 as syenite, areas in which this rock constitutes more than 50 per 

 cent of the whole, and as Grenville those in which the syenite con- 

 stitutes less than 50 per cent. 



The syenites have been described in detail, with chemical analyses 

 in so many of the New York State Museum bulletins that it seems 

 superfluous to repeat the discussion here.- As shown on the quad- 

 rangle. the\' are usually greenish gray rocks, sometimes blotched 

 with red and grading into varieties richer in (juartz and wholly 

 red. The rock is thoroughly gneissoid. The most interesting thing 

 about it is the way in which it uniformly runs over into coarsely 

 p()r])h\ritic \arieties at the margins and in the dikes of syenite in 

 the (irenville. 'J'he p()rph}'ritic crxstals, usually called augen, are 

 often large, reaching a length of 2 inches, while those of an inch 

 in length are very common ; the feldsi)ar of these augen is usually 

 red. the augen are aligned parallel to the foliation, and in many 

 cases are ])artly or wholly crushed or granulated. Jn the bod}' of 

 the rock, mica has developed in quantity and the resemblance to a 

 metamorphosed conglomerate is strong. 'JMie rock is considerabl\- 

 more (juartzose and acid than the main body of the syenite. 



In the description of the Alexandria syenite of the Alexandria 

 (juadrangle, a similar por])h\ ritic, marginal phase of the rock was 

 described, but some (jonbt was expressed as to whether it was in 



' W. J. Miller, map acconipanyiii.u \. \'. .Stale Mus. lliil. 1 3,v 

 -' I'.iil. <)5, p. .^IJ 40; r.ul. 115, 11.51-' -'5: I'.nl. i.^*^. p. 44 5J ; I'.nl. 145, p. 

 i8j 84 ; I)ul. 15,?, p. 14 21. 



