GEOLOGY OF THE WEST POINT OIIADR ANGLE, NEW YORK 12 



of arkoses or acid volcanic Lul'ts. The complex is invaded by ga'bbros, and 

 by rocks called syenites that are practically identical with the Byram gneiss 

 in New Jersey. 



The principal formations recognized by the geologists working in 

 New Jersey are : 



a The Franklin limestone (oldest) together with scattering 

 lemnants of metamorphosed sediments of other compositions such 

 as quartzites and micaceous schists, representing the oldest series 

 but mapped with other larger units. 



b The Pochuck gneiss (next in age) a basic gneiss of very vari- 

 able habit and probably both sedimentary and igneous origin. This 

 is judged to correspond to the basic gneiss development of the West 

 Point area, such as the belt at Peekskill, and to the meta gabbros 

 and associated injection gneisses of the Adirondacks. This type 

 is more pronounced in the Franklin Furnace area than in the West 

 Point quadrangle. 



c The Losee gneiss (apparently younger than the Pochuck). 

 A series of very variable granite gneisses with gradational relations 

 to almost everything else in the region. It is not certain that any 

 of the formational units of the West Point area correspond ver}^ 

 closely to the Losee of New Jersey ; but perhaps the Canada Hill 

 type represents the same general historical step. 



b The Byram gneiss (the youngest meniber). This term covers 

 a considerable variet}- of items according to the New Jersey geolo- 

 gists, but descriptions of its chief microscopic characters emphasize 

 the constancy of certain mineral make-up and habit that suggest a 

 possible relationship to the Storm King granite of the West Point 

 area and the syenite of the Adirondacks. It is evident, however, if 

 this correlation is correct, that the Byram gneiss formation is more 

 confused in age and structural relation than are its equivalents 

 farther north. Probably a closer correlation can not be made because 

 of the different points of view of the different workers as to the 

 chief formational distinctions and their significance. 



Summary of the Netv Jersey correlation. The effort to correlate 

 with the mapped districts of northern New Jersey has not been very 

 successful. Doubtless the remnants of ancient sediments, now 

 heavily metamorphosed and all but swallowed up in the igneous 

 invasions, are the equivalent of the Grenville as used in this bulletin 

 for similar remnants. 



The Pochuck gneiss is probably also roughly equivalent to certain 

 less prominently developed basic gneisses of the West Point quad- 



