O NEW YORK STATE MUSEUM 



Probably few districts can be found anywhere better illustrating 

 the problem of petrogenesis of the mixed gneisses, and this one can 

 not be described at all without undertaking such discussion. 



We have, therefore, accepted the situation as it is and have devoted 

 our best effort largely tO' an exposition of the origin and character 

 and relation of such rocks belonging to the West Point district, — 

 the now complex ancient sediments, the almost equally complex 

 igneous members which are everywhere intimately related to them, 

 and those still more complex and obscure rocks whose features in 

 part resemble both the sediments and the igneous types and which 

 are confidently believed to be actual mixtures. The bulletin there- 

 fore is only in part a description of the West Point quadrangle. To 

 almost an equal degree it is a discussion of the principles involved 

 in the origin of our oldest and most complex rocks. 



Work was originally begun by the senior author of this paper on 

 the Tarrytown quadrangle and a manuscript map has been in exist- 

 ence for many years. Before that work was finished, however, the 

 investigations for the Catskill aqueduct began and new data of 

 importance accumulated so rapidly that it was thought best to delay 

 at least till full advantage could be secured from that study. Later 

 it became apparent that the West Point area held more critical 

 geological material bearing on the origin and correlation of the 

 crystalline schists and gneisses than does the Tarrytown quadrangle. 

 It was finally decided to accept this situation and issue the West 

 Point bulletin first using it as a key discussion of the major genetic 

 and structural problems of the region of crystalline rocks of south- 

 eastern New York. 



It is not practicable to indicate individual responsibility for the 

 different parts of this bulletin or for the departures from the usual 

 treatment that it may contain. 



The bulletin is a consistent attempt of a teacher and investigator 

 of several years' experience in the district to cooperate with a junior 

 associate whose insight into complex geologic problems and whose 

 enthusiasm for field work has made it possible to finish a study 

 begun long ago. 



