GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK ICQ 



outbreak is found. Thus it might happen repeatedly, each titae with 

 some prospect of finding similar igneous behavior and to some 

 degree similar petrographic quality in widely separated localities. 

 Such a result, it seems, would be most unlikely without some 

 sufficiently widely distributed, very fundamental, deep-seated single 

 unit to be regarded as the chief manufacturer of the whole igneous 

 history. Only on such a basis do we feel a»y confidence in suggest- 

 ing the correlation referred to in detail in a later paragraph where the 

 Canada Hill granite of this area is correlated with the Losee gneiss of 

 New Jersey and with the older granite of the Adirondacks or when 

 the Storm King granite of this area is correlated with the Byram 

 gneiss of New Jersey and the Syenite series of the Adirondacks. 



Such a genetic connection of the principal igneous members should 

 develop the intimate mineralogic and structural gradations and con- 

 fused and obscure transitions, which characterize many of these 

 units, and it ought to yield a number of minor units of related 

 origin, but with very great mineralogic differences. Such gradations 

 and confusions ought to be expected, under the condition assumed, 

 because the members are all of the same origin and form a genetic 

 series between which there are no breaks beyond such as develop 

 marginally during stages of quiescence or where successive indi- 

 vidual apophyses invade country rock as separate units. All the 

 older granite members, therefore, of this quadrangle seem to belong 

 to a single igneous history and are simply the different expressions 

 connected with the development of a single bathylith. 



To this particular history belong the Canada Hill, the Reservoir, 

 the Mahopac and the Storm King granites. Doubtless also some of 

 the more basic rocks are of the same origin and represent extreme 

 differentiates only. Even some of the magnetite bands or magnetite- 

 bearing pegmatites are probably of the same connection. 



It is not clear, however, that this is the very oldest igneous history. 

 There are basic gneisses, essentially dioritic in composition, 

 intimately associated with the Grenville that exhibit the schistose and 

 gneissic structure more strikingly than most of the granites, and it is 

 probable that certain of these dioritic units are older than the first 

 granite. These may be referred to under the general term Pochuck 

 diorite. 



,No good means of determining how much of a break there is 

 between them has been discovered. The best evidence that we 

 have is in connection with the Reservoir granite and the bands of 

 dioritic gneiss developed in the vicinity of Peekskill and further to 



