GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK II9 



Postglacial changes are wholly of the nature of erosion. There has 

 been some reelevation of the land so that terraces judged to date 

 from the time of the recession of the ice are now lifted somewhat 

 above sea level. On the rocks of such a region as this, however, 

 and even on the type of glacial deposits represented, there is little 

 modification produced in this time. 



On account of the fact that the details of glacial history and in 

 large part also of the late Tertiary history are bound up with the 

 development of the physiography of the region, the rest of this dis- 

 cussion is included with the physiography. 



Correlation Problems 



Two entirely distinct problems of correlation are presented by 

 the formations of this quadrangle. 



1 One is concerned with the comparison of the Precambrian 

 gneisses and granites, and the succession of events represented by 

 these units in this district, with other districts where the succession 

 may be either better known or have a somewhat clearer expression. 



2 The other problem is concerned with the possible identity of the 

 Hudson River- Wappinger-Poughquag series of Cambro-Ordovician 

 sediments, extensively developed north of the Highlands, and the 

 Manhattan-Inwood-Lowerre series of crystalline schists, marbles 

 and quarzites south of the Highlands. 



In the first problem, that of the gneisses and granites, the areas to 

 be compared lie far apart and appear to be hopelessly separated 

 from each other by intervening formations. In the second case, that 

 of the Cambro-Ordovician correlation, representatives of the two 

 series come within the bounds of this quadrangle and patches of the 

 two contrasted series lie within a mile or two of each other. In 

 neither case, however, can the problem be solved by tracing the one 

 series directly into the other and, consequently, correlation must be 

 based on comparison of major critical characters and similarity of 

 history. 



I The Precambrian gneisses and granites. In this problem of 

 the Precambrian gneisses and granites it is especially desirable to 

 make comparison with the Adirondacks, where not only has a great 

 amount of detailed work been done, but the geology is fairly well 

 established in the same terms that have come into use in the much 

 oreater Precambrian fields of Canada. 



Similar work has been done also within the Highlands belt in New 

 Jersey, represented by the Franklin Furnace and the Raritan folio#. 

 ij, S. G. S. Nos. 161 and 162. 



