110 Prof. J. D. Dana — Metaniorphum of 



in. — On a Case in which various massive Crystalline Eocks 

 INCLUDING Soda-Granite, Quartz-Diorite, Norite, Horn- 

 blendite, Pyroxenite, and different Chrysolitic Eocks, 

 WERE made through Metamorphic Agencies in one Meta- 

 MORPHic Process. 



By Prof. James D. Dana, LL.D., A.M., For. Memb. Geol. Soc. Loud., 



of Yale College, New Haven, Ct., U.S.A. 



Part II. 



(Continued from page 65.) 



B. The Eelation op the Cortland Eocks to the other Eocks of "West- 

 chester County. 



THE above brief descrijDtion of the Cortland rocks prepares the 

 way for a consideration of their relation to the other rocks of the 

 county. The following questions arise: Are they one with the latter 

 in system ? are they rocks of an earlier system? or are they eruptive 

 rocks, and not metamorphic, and hence, of no bearing on the general 

 question as to the age of the Westchester limestones and the asso- 

 ciated schists ? 



1. Evidences of more or less Complete Fusion. 



The evidences of fusion or plasticity are many ; and, taking them 

 collectively, they are decisive. They are exhibited in the following 

 ways: (1) The massive character of the crystalline rocks over so 

 large an area, and a general resemblance in them to igneous rocks ; 

 (2) the great size of the hornblende crystals in some of the qnartz- 

 diorite, and the well-defined crystals of hypersthene in part of the 

 norite, resembling the augite crystals of some volcanic rocks, facts 

 indicating freedom of molecular movement during the process of 

 crystallization ; (3) the broken condition of the crystalline indi- 

 viduals in some places, which is evidence of movement while in a 

 pasty state after the beginning of solidification ; (4) the occurrence 

 in the massive rocks of included fragments of other rocks, like the 

 inclusions in many trap or basaltic ejections : (5) the existence of 

 dykes or veins of the hornblendic and other rocks, of very various 

 sizes, intersecting the adjoining rocks. 



The inclusions are remarkably numerous in some portions of the 

 region, and are often of wonderful magnitude. About Cruger's 

 station, in the soda-granite and quartz-diorite, they occur from an 

 inch in breadth to many feet ; one seen in the face of a bluff on the 

 railroad, between three and four hundred yards north-east of Cruger's 

 station, has a maximum breadth of eighteen feet and a length but 

 little less, and consists of garnetiferous mica-schist like that within 

 a fourth of a mile to the east and south ; and this is not the largest 

 in that region. They abound also in the chrysolite rocks and norite 

 of Montrose Point and Stony Point, and in the limestone of Ver- 

 planck Point. They usually consist of the various materials which 

 constitute the schist of the vicinity, even to the magnetitic garnet 

 rock, quartzite, etc. 



