GfiOLOGY OF tl-IE WEST POINT QUADRANGLE, NEW YORK 33 



which is involved with the igneous history itself. It seems certain, 

 however, that these rocks have derived more character from their 

 igneous relations than from their earlier metamorphic history. 



On the whole, the simpler formations, such as the Hudson- 

 Wappinger-Poughquag series, represent comparatively straight- 

 forward dynamic history and the sort of metamorphism that belongs 

 to recrystallization of rocks under no very enormous load. There 

 is much distortion, faulting, dislocation and flow of the softer 

 members and differential movement between the more competent 

 members, with the usual development of slates, crumpled phyllites, 

 crush breccias and somewhat recrystallized limestones and quartzites. 



In contrast, the Manhattan-Inwood series represents most elabo- 

 rate recrystallization under sufficient load to accomplish complete 

 reorganization, and development of high density minerals such as 

 garnet. Mica schist, hornblende schist, limestone schist, quartz 

 schist and crystalline limestone of coarse marble habit are not 

 unusual — apparently recrystallized under dynamic influence. 

 This condition prevails even where igneous phenomena are not 

 apparent and it is therefore believed that it is not necessarily con- 

 nected with that influence. But it is, at many other points, associated 

 with igneous phenomena which do give the effects already emphasized 

 in this type. 



In the older series, the Grenville, occasional members are little 

 affected by injection and impregnation from igneous sources, but 

 the formation, as a whole, is very extensively involved. There is 

 much silication of the limestone with decarbonation and development 

 of graphite already described. 



Original magmatic difference. The variations in rock quality 

 caused by original differences of the invading magmas are not so 

 great as those due to other causes, but there are differences of this 

 sort and some of the peculiarities of petrographic quality are con- 

 nected with them. It appears, for example, that certain of the 

 magmatic units were exceptionally capable of invading the surround- 

 ing or overlying country rocks in an insidious and pervading way 

 so as to mix intimately and extensively with these older members. 

 This is particularly true of the " Canada Hill " type of granite 

 which, as interpreted by us, was capable of penetrating all the weak- 

 nesses of the adjacent rock and introducing its own minerals, and 

 also of absorbing great portions of this same country rock and 

 incorporating it in its own magma. Sometimes, doubtless, nothing 

 of the original has been preserved, but in other cases, something of 



