GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK y\ 



under movement, as suggested by many writers on such phenomena, 

 but this is not so clear. It is certain, however, that differentiation has 

 some structural possibiUties, and this is clearest with the pegmatitic 

 facies. Nowhere in the Highlands does there seem to be such a 

 thing as a segregation mass, such as a marginal ore, but that separa- 

 tions of this kind probably did take place is indicated by the occur- 

 rence of magnetite bands of pegmatitic habit which appear to have 

 been injected. 



The features referred to in the foregoing paragraphs make up 

 >vhat has been referred to elsewhere as the structural confusion of 

 these older formations. Other features than those mentioned may 

 be encountered but they are all believed to be of the same general 

 genetic meaning. 



Forms Represented by the Individual Units 



In the series of formations mapped, some are sedimentary beds 

 and have a distribution characteristic of such beds modified by the 

 deformations which are included in their subsequent history. 



The Hudson River- Wappinger-Poughquag series, the Manhattan- 

 Inwood-Lowerre series and Grenville formation were primarily 

 sedimentary. Except in the case of the Hudson River- Wappinger- 

 Poughquag series the original structural habit is much obscured by 

 subsequent metamorphic and igneous history. This obscurity is 

 developed to an extreme in the Grenville where a large part of the 

 original bedding is completely destroyed and only the secondary 

 structural habit is preserved. Enough remains, however, to prove 

 that bedding was a fundamental structure in this oldest formation 

 of the region. 



The igneous formations occur in a variety of structures, some 

 of which are bosses and perhaps others are laccolithic or sill-like. 

 The behavior of the Canada Hill granite suggests bathylithic rela- 

 tions. Nearly all the igneous masses conform more or less to the 

 trend of the region and the primary control of this trend is undoubt- 

 edly the structure of the Grenville. All the larger masses have such 

 relation and form, but a far greater variety of form is represented 

 by smaller units, too small in fact to be mapped. These are the 

 injection bands and stringers as well as dikes and veins which 

 cut through the earlier rock constituting the inclosing walls. The 

 most clearly marked units of this kind are dikes, but their promi- 

 nence and importance are insignificant compared to the abundance 

 of the pegmatite bunches and stringers, the veins and the injection 

 bands. 



