GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK I39 



graphic habit of the two series, especially of the upper- 

 most members. 



2 General absence of the quartzite or lower member on the 



south side of the Highlands with the metamorphosed series. 



3 Absence of as definite bedding and granular structure in the 



Manhattan as ought to be expected if it is the metamorphic 

 equivalent of the Hudson River formation. 



4 Prominence of igneous impregnation in the Manhattan and 



absence of igneous influence in the Hudson River forma- 

 tion. 



5 Striking unconformity between the Poughquag and the 



gneisses on the north side, contrasted with the apparent 

 conformity of the Inwood and the Fordham gneiss of the 

 south side of the Highlands. 



6 Occurrence of an interbedded layer of typical gneiss in the 



Inwood limestone member not far above its base. 



7 The petrographic make-up of the Hudson River graywackes 



and other coarse-grained beds, which indicates derivation 

 from the destruction of preexisting somewhat meta- 

 morphosed sediments rather than from gneisses and 

 granites, and the fact that the Manhattan-Inwood-Lowerre 

 series would meet the requirements of such a source better 

 than any other now represented. 



8 The evidence presented by the metamorphic condition of the 



Manhattan schist of a greater load of overlying sediments 

 than would have been available if it is the equivalent of the 

 Hudson River formation. 

 On the basis of these facts of observation and statement of rela- 

 tion it seems preferable to continue to regard these two series as 

 distinct and separate and of very different age. The facts are 

 stated in as unprejudiced a manner as possible rather than in the 

 form of a completed argument, knowing that the problem will still 

 be regarded as an unsettled one and that it will necessarily attract the 

 attention of every worker on areal and structural geology in the 

 crystallines of southeastern New York and adjacent districts. That 

 additional data will be furnished from detailed study of neighbor- 

 ing areas is certain, and perhaps they will be more convincing than 

 those listed above, but in any case a fair statement of the facts now 

 available may be of service toward a final and more generally accepted 

 solution. 



10 



