248 W.J. MILLER MAGMATIC DIFFEREXTIATIOX AlTD ASSLSIILATION 



ducing green and red mottled rocks. FLoaUy, the red predomiiiates and the 

 rock becomes a distinct granite." ^ 



Observations of I. H. OgUvie. — Ogilvie states, concerning the syenite 

 and granite of the Paradox Lake quadrangle, that — 



"Both in this region and elsewhere the syenite is bordered by granite, the 



granite being much more gneissic than the syenite. Gradations between the 

 two are common. It seems most reasonable to regard the granite as a border 

 development of the syenite, derived from the same magma." * 



Observations of J. F. Kemp. — Kemp says of the syenite series of the 

 Elizabethtown and Port Henry quadrangles : 



•There are phases, apparently differentiation products of the syenite magma, 

 in which it (quartz) is very abundant, and the rock becomes a (reddish) gran- 

 ite or of granitic composition. . . . Again, in the basic extremes, it fails, 

 and in the true syenite phases, the most characteristic of the series, it is rare 

 or absent" * 



Observations of the writer. — The writer has made many observations on 

 differentiation throughout the southern Adirondack region, but only a 

 few of the most decisive, carefully studied examples will here be men- 

 tioned. 



In the Port Leyden quadrangle^^ the normal syenite clearly grades into 

 a red granitic gneiss, it beiog impossible to draw sharp lines of separation 

 between them in the field. It seems certain that this red granitic gneiss 

 is a differentiation phase of the normal syenite. Except for the greater 

 granulation, somewhat higher quartz content, and red hematite stains of 

 the granite, microscopic study shows no essential difference between the 

 two rocks. 



In the Broadalbin quadrangle,-^ west of Sacandaga Park, a typical 

 pink granite porphyry, with prominent porphyritic texture, high quartz 

 content, presence of biotite and absence of hornblende, grades into a 

 typical, medium graiued, moderately quartzose hornblende syenite. The 

 clearly exhibited field relations, microscopic study of the transition rocks 

 and very closely related chemical compositions prove that these two 

 rocks, so different in appearanc-e, are reaUy only differentiation products 

 from the same cooling magma. 



In the Lake Pleasant quadrangle^^ the writer has studied, in the field 



' H. p. Gushing : X. T. State Mus. BuU. 115, 1907, pp. 477-478. 



8 1. H. OgilTie : X. Y. State Mas, BnU. 96, 1905, p. 503. 



• J. F. Kemp : X. T. State Mus. BulL 138, 1910, pp. 46-47. 



»W. J. MUler: N. Y. State Mus. BuU. 135, 1910, pp. 15 and 17. 



" W. J. MiUer : N. Y. State Mus. BuU. 153. 1911, pp. 18 and 20. 



" W. J. Miller : Geology of the La^e Pleasant Quadrangle ; in preparation. 



