GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK 41 



spaces between the grains of the older rock and of penetrating its 

 most minute structural imperfections and, in extreme cases, of liter- 

 ally saturating the original rock. In its simplest form this process 

 resembles induration and silicification where materials are simply- 

 added. In its somewhat more elaborate form it is a selective replace- 

 ment. In its most complicated development it is accompanied by 

 absorption, by replacement and by contact metamorphic effects which 

 transform the original rock into a mixed product. This is in part 

 made up of remnants of former minerals, in part of syntectic 

 products, and in part of materials that represent the invading 

 igneous masses. 



Doubtless very fluid condition and high content of mineralizers 

 or emanations, together with high temperature and great depth or 

 pressure, are conditions favorable to su<ih type of penetration. 

 Certainly not all igneous masses exhibit any such tendency in their 

 field occurrence, but some of them do and an occasional one exhibits 

 this behavior to a very exceptional degree. The most efficient unit 

 in the West Point area seems to be the Canada Hill granite. It has 

 been mentioned before as showing competence . in absorbing the 

 surrounding rock, but it probably was equally vigorous in sending 

 out invading substances which penetrated the older Grenville series 

 most complexly. . It thus happens that it is impossible in some places 

 to decide between the conflicting possibilities of rock origin, because 

 the rock may be partly metamorphosed sediment and partly true 

 igneous. These two representatives have so intimately intergrown 

 that the rock is now as simple looking as some of the direct differen- 

 tiation products or some of the metamorphics. The types! of 

 original rocks most readily invaded in this way seem to have been 

 the granular f ragmental ones or the shaly or schistose ones, but the 

 effect is sometimes noticed even in the limestones, and it is not 

 unusual to find an a:bnormal carbonate content in a rock that other- 

 wise looks like a granite gneiss. Such rocks should be called grani- 

 tized rocks if the invading sulbstance is of granite composition, but 

 there seems to be no general term for the process as applied to all 

 magmas. Granitization, however, stands reasonably well for the 

 results secured in this district, because certain of the granites give 

 the most conspicuous examples of the working of the process. 

 Farther to the south the same habit appears in connection with 

 pegmatite development in certain portions of the Manhattan schist. 

 These pegmatites have soaked through the schist in an almost 

 unbelievable way and to such large amount that in places the schist 



