256 W. J. MILLER MAGMATIC DIFFERENTIATION AND ASSIMILATION 



sions, from a few feet to a few rods long, which have been either par- 

 tially or wholly fused and melted into the syenite or granite. Very fine 

 examples occur 1-J miles northeast of the summit of Kelm Mountain 

 (North Creek quadrangle)/^ where inclusions of dark, garnetiferous, 

 Grenville gneiss show perfect gradations, through zones of a few feet, 

 into the inclosing granite porphyry. The intermediate rock is coarse 

 grained, very garnetiferous, and not so porphyritic as the true granite 

 porphyry. 



Another example, typical of many similar occurrences, is a single rock 

 ledge, 40 feet across, 1 mile due southeast of the summit of Hamilton 

 Mountain (Lake Pleasant quadrangle), where the intimate relationships 

 of dioritic, granitic syenitic, granitic, and Grenville gneisses are clearly 

 exhibited. In the accompanying table the compositions of these gneisses, 

 except the Grenville, are shown : 





<s> 



a> 









0/ 



<^ 

















"c 







TS 



c 











o 



CS 



j^ 



a 







s 



1 o> 



•^ 







<!' 



'Z^ 



CI 





-«; 



^5• 



a> 



« 



ijs 



<» 



® 



• 





00 



o 



O 



i 



O 







o 



IXl 





c 



1 



o 





24 



5 







55 



13 



7 



18 





1 



1 



little 







23 



45 







23 



22 



3 





5 



1% 



% 



little 





21 



25 



38 



5 



27 



8 







1 



X 



X 



little 











Number 24 is a rather basic (dioritic) rock greatly resembling certain 

 phases of basic syenite; number 23 is a granitic syenite, and number 21 

 is a good pink granite. These typesi grade back and forth into each other 

 several times in this one outcrop. There are many narrow streaks, layers 

 or inclusions of Grenville dark, biotite-feldspar gneisses sometimes con- 

 taining garnets. At times these streaks are pretty clearly defined, while 

 again they are not, but always, though often locally twisted, they roughly 

 follow the gneissic bands. The texture and composition, especially of 

 the granite, vary considerably, and a few garnets occur sporadically in 

 the syenite and granite. The ledge is perfectly bare, with relationships 

 well exhibited, and it is certain that the dark, dioritic bands or streaks 

 are Grenville which have been more or less fused into the molten granite. 

 Where thoroughly assimilated, the basic rocks have resulted, and where 

 not thoroughly fused in the streaks are still visible. Every stage of the 

 assimilation process is shown. 



23 W. J. Miller : N. Y. State Mus. Bull. 170, 1914, p. 23. 



