GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK 39 



has been crudely preserved after the rock which it represents has 

 been otherwise wholly destroyed; and it is a result of the failure 

 to redistribute completely its chemical components rather than a 

 peculiarly efficient assembling of them. 



It is believed that this principle is represented on a very large 

 scale and, to some degree, in all the formations appearing as invading 

 igneous masses. Even the Cortlandt series has its representatives 

 of this sort, as advocated many years ago by the senior author of 

 this bulletin in explanation of the meaning of the emery deposits 

 and their peculiar structural and compositional features. 



The most striking representative of this habit, however, is, we 

 believe, the type designated in this paper, the Canada Hill granite. 

 This type, as already indicated in an earlier paragraph, seems to 

 have been especially competent and vigorous, both as an insidious 

 invader of adjacent country rock and as an absorber of incorporated 

 blocks from the same source. The gradation is so complete in all 

 stages between these two extremes of behavior that it is impossible 

 to determine where the invaded rock, still retaining some of its old 

 composition, stops, and the absorbed rock, representing a syntexis 

 with nothing left but the so-called antecedent structure, begins. 

 That both are largely represented we feel certain but the appearance 

 is so similar and .the structure and composition, even in minor detail, 

 are so nearly alike that no adequate criteria have yet been discovered 

 for their discrimination. Here again, an understanding apprecia- 

 tion of a principle or process is a great satisfaction and aid in inter- 

 pretation of the complexities encountered in the field, but accurate 

 discrimination between individual specimens is often impossible. 



Igneous injection. It is well understood that certain very fluid 

 types of igneous magmas show great vigor in invading adjacent 

 rock, and seem to find all sorts of obscure weaknesses along which 

 to thrust themselves. In a general way, even those magmas not 

 strikingly capable in this direction are able to penetrate or cut 

 through overlying or adjacent formations. In this sense, all the 

 igneous masses in this quadrangle are intrusions, but only those 

 of comparatively high fluidity succeed in penetrating vigorously 

 enough to become distributed in small masses through long distances. 

 Such a tendency normally develops a striking banded habit if the 

 injections are repeated or occur at small intervals, and results in 

 the so-called lit-par-lit injection structm-es. Such action is not con- 

 fined, of course, to a single invading magma or to a single epoch, 

 and in a district with as complicated a history as this, such injection 



