THE CRYSTALLIZATION OF IGNEOUS ROCK 177 



crystallization-differentiation of batholithic masses as to serve as 

 carriers for magnetite, and to act at the same time as granitizing 

 agents and producers of magnetite-ore bodies.^ In these cases the 

 country-rock may be so flooded with quartz, or quartz and feldspar 

 from igneous sources, as to profoundly change the character of the 

 invaded rocks without causing any of the phenomena just mentioned 

 to ensue. As an example of this action on a very small scale, the 

 effect of the intrusion of the Palisades diabase on some portion of the 

 adjacent arkose may be mentioned. The original clastic grains of 

 feldspar seem to have been detached and in small part recrystallized, 

 the original grains of quartz appear to have been merged with and 

 taken into the substance of the invading end-stage quartz derived 

 from the igneous mass itself, so that the feldspar grains of the 

 arkose are set, in a sort of poikilitic fashion, in a matrix of much 

 more coarsely crystalline quartz behaving as a mosaic of larger 

 unit grains. An attempt has been made to show this in Figure 10. 

 In connection with the magnetite ore-bodies of southeastern 

 New York, there is an occurrence of extremely coarse and very acid 

 granite, always intimately associated with the ore-bodies and usually 

 best and most extensively developed immediately adjacent to them. 

 Field and petrographic study shows that these "granites," which 

 the writer has called Pochuck granite, are merely end-stage quartz, 

 with in some cases feldspar, carrying partially assimilated frag- 

 ments of the country rock (Pochuck- Grenville), and represent- 

 ing the very extreme end-phase product of the same general 

 processes which produced the magnetite. Figures 1 1 and 1 2 illus- 

 trate two of them; Figure 11 is from the vicinity of the Clove 

 mine. Figure 12 is adjacent to the Forest of Dean Mine, Orange 

 County, New York. Both samples were taken at the surface. 

 It will be observed that they are very largely quartz with a few 

 scattered, partially assimilated fragments of country-rock (Pochuck- 

 Grenville). Where the Pochuck- Grenville was more calcareous, 

 and especially where the emanations encountered actual inter- 

 bedded limestone (Grenville), characteristic lime-contact minerals 

 were formed, although the interbedded limestone itself may have 



' R. J. Colony, The Magnetite Deposits of Southeastern New York. To be published 

 as a bulletin of the New York State Museum. 



