OCCLUSION OF IGNEOUS ROCK 405 



biotite schist and gneiss, and sometimes steatite. In the horn- 

 blendites at New Rochelle and Rye, aggregates of iron-garnet, 

 up to 5 cm. in length, may imply the result of contact reaction 

 between the intrusive rock and adjoining schist. That this re- 

 action has not involved the magnesian limestone of the vicinity, 

 is shown by the absence of lime garnet. 



As to the huge boss of granodiorite, seven miles in length, 

 in the town of Harrison, the described mineralogical constitu- 

 tion^ indicates that this is but a phase of the granite and mon- 

 zonite of the State Line belt in Pennsylvania.'^ Transition forms 

 by metamorphism appear in the fringe of hornblendic gneisses 

 around that area and perhaps the great tract of augen-gneiss 

 in Bedford. 



Passing northward, outcrops of hornblende schist and diorite 

 are met, first reported by Credner, and of gabbros, as at the 

 new Croton Dam, with large pegmatite dikes in Bedford, as well 

 as the common seams and lenses of the earlier pegmatite in- 

 trusion. 



At the northern end of the county, the well known Cort- 

 landt Series occurs on the southern part of Montrose Point, 

 below Peekskill, as well as across the Hudson river at Stony 

 Point, and at Rosetown, a little further west. This covers an 

 area of about 25 square miles and comprises the following rocks : 

 peridotite (cortlandtite and pikrite) ; norite with hypersthene 

 (also hornblende-norite, mica-norite, augite-norite or hyperite, 

 and pyroxenite); gabbro (with mica-gabbro and gabbro-diorite); 

 diorite (with brown hornblende-diorite, hornblendite, green 

 hornblende-diorite, mica-hornblende diorite) ; mica-diorite (with 

 hornblendic and hypersthenic varieties). Diabase has also been 

 reported, and the ultra-basic rocks, magnetite, emery and her- 

 cynite, besides metamorphic representatives in the hornblendic 

 gneisses. Dikes occur, cutting through peridotite, norite and 

 limestone, at Montrose, Verplanck and Stony Points.^ In the 

 Rosetown series, also, numerous small dikes are found around 



1 H. Ries, Trans. N. V. Acod. Set., XIX, 1895, 80-86. 



2 F. Bascom, /oc. cit., 102. 



sj. D. Dana, Am. Jour. Sci., (3), XX, 1880, 202. 



