254 Williams — Contact-metamorphism near Peek-skill. 



Art. XX YI. — The Contact-Metamorphism produced in the 

 adjoining Mica schists and Limestones hy the Massive 

 Pocks of the " Cortlandt Series" near Peekskill, W. Y. ; 

 by Geouge H. Williams. With Plate YI. 



Lsr three former papers I have described the principal types 

 and some of the intermediate varieties forming the complicated 

 group of massive rocks known as the " Cortlandt Series."* 

 Aside from their own intrinsic interest, these rocks are hardly 

 less worthy of attention on account of the unusual contact- 

 metamorphism which they have occasioned in the adjoining 

 schists. 



The area occupied by the Cortlandt massive rocks — about 

 twenty-five square miles in extent — is bordered on the south 

 mainly by mica schists and on the west mainly by limestones. 

 Both of these rocks have been altered by the masses which 

 have broken through them, although the metamorphosing in- 

 fluence has not extended far from the contact. The gneisses, 

 on the other hand, which border the Cortlandt area on the 

 north, do not appear to have been materially affected. 



The two localities where the^e phases of metamorphism were 

 best observed — both already known through Professor Dana's 

 descriptions of them — are here selected as typical. A further 

 search would doubtless reveal other localities as interesting, 

 while the emery and iron (pleonaste) deposits already described 

 by the writer as occurring in the southern part of the Cort- 

 landt area,f may with certainty be referred to the same category. 



The two typical localities referred to are : for mica schist 

 metamorphism, Cruger's Station; for limestone metamorphism, 

 southern end of Yerplauck Point. 



I. Contact-metamorphism in the Mica Schist. 



If we leave the train at Cruger's, a station on the Hudson 

 River Railroad about four miles south of Peekskill, we find 

 ourselves near the river-bank which at this point extends nearly 

 west for about three fourths of a mile. Near the shore the 

 rocks exposed are mica schists, but these are frequently covered 

 by beds of clay which is used in the numerous brick-sheds 

 of this region. Not over a few hundred yards from the shore 

 rises a rocky wall which extends nearly parallel to the river 

 bank until this bends toward the north. This wall coincides 

 with the southern edge of the massive rocks of the " Cortlandt 



* This Journal, III, xxxi, p. 26, Jan., 1886; ib., xxxiii, pp. 135 and 191, Feb. 

 and March, 1887; ib., xxxv, p. 438, June, 1888. 

 \ This Journal, III, xxxiii, p. 194, March, 1887. 



