66 NEW YORK STATE MUSEUM 



The gray color, on the other hand, is most frequently the product 

 of atmospheric alteration, and in numerous places can be observed 

 to grade within the depth of a few inches into the normal pink 

 type ; or again, its development is even more shallow and is restricted 

 to thin exfoliated shells which on peeling oil disclose the flesh- 

 colored fresh rock beneath. This, however, 'does not apply to those 

 thin, grayish zones which generally surround or border the amphi- 

 bolite inclusions caught up by the granite, and for which it is diffi- 

 cult to offer a precise explanation (see plate lo, upper figure). The 

 granite has in such cases been deprived of its small content of pig- 

 ment, but whether through a local reduction to magnetite, which is 

 not abundant, or through a migration of the femic molecules toward 

 and into the xenolith, it is impossible to say, as no special study of 

 this point was made. . It is, however, possible that we have here an 

 illustration of the transfusion of the basic molecules of the granite 

 into the altered limestone xenoliths (assuming the inclusions to be of 

 this origin), a physico-chemical hypothesis proposed by Adams and 

 Barlow to account for the transmutation of limestone into amphi- 

 bolite by granite. If operative at all. however, this process must 

 have gone on to a very slight degree only, as the bleached margin of 

 granite surrounding the xenoliths is nowhere over 2 or 3 inches 

 broad, and at best the iron content derived in this way must be a 

 very inconsiderable proportion of the total femic content of the 

 highly ferromagnesian inclusions. 



In this connection, it is to be observed that the limestones in 

 general can not be observ'ed to show the well-marked bleaching 

 effects upon the pink granite gneiss, which, as obser\'ed by Pro- 

 fessors Gushing and Smyth (Gushing et al. 1910, pages 46-47), 

 are so well marked in other outlying localities on this side of the 

 Adirondacks. This fact can not be accounted for by any notable 

 differences in the geological conditions. Although actual exposed 

 granite-limestone contacts are not common in the area studied, out- 

 crops of these formations are frequently found within a few feet 

 of each other, but in no case was the granite observed to lose its 

 characteristic pink color within the exposed limits of the outcrops. 



That the process may have been operative to a certain extent, 

 however, is shown by the uniformly white color of the narrow 

 pegmatite dikes cutting limestone or calcareous schists, in contra- 

 distinction to the occasional ruddy or pink color of those intruded 

 into siliceous and ferromagnesian schists. This contrast can be well 

 observed on comparing the red granite dike at the south end of the 





