266 Williams — Contact-metamorphism near Peeks-kill. 



Lossen and Koch also mention cordierite as an abundant 

 constituent in the kersantite of Miehaelstein, although this 

 mineral does not appear in the inclusions.* 



II. Contact-metamorphism in the Limestone. 



The limestone beds associated with the gneisses and mica 

 schists of "Westchester County have been carefully mapped and 

 described by Professor James D. Dana.+ They are regarded by 

 him as belonging to the Green Mountain system and as probably 

 of Lower Silurian or Cambrian age. Some of this limestone 

 appears within the limits of Cortlandt township, but it falls 

 within the scope of this paper only in so far as it has been 

 modified by the action of the intrusive rocks of the Cortlandt 

 Series. 



The western edge of Terplanck Point, which projects into 

 the Hudson Piver south of Peekskill, is formed of the Tomp- 

 kins Cove limestone, so admirably exposed in the large quarries 

 on the opposite side of the river. At the southern end of the 

 point the limestone is in contact with the massive rocks, which 

 here display in the most unmistakable manner the evidence of 

 their eruptive character. This fact is admitted by Professor 

 Dana, although he is inclined to regard the dykes there exposed 

 as softened or fused sedimentary material rather than truly 

 exotic intrusives4 



* At the close of his series of articles on the Westchester County rocks. Pro- 

 fessor Dana has very admirably summarized all the essential contact phenomena 

 displayed at Cruger's. (This Journal. III. xxii. p. 314. Oct. 1881.) He here also 

 advances four considerations which he believes to be adverse to the idea that the 

 contact-phenomena were produced by the action of an eruptive rock. These con- 

 siderations are briefly as follows: 



1. The crumpling of the schist must have been produced at the time of its 

 metamorphism. 



2. An intruded rock would have been too feeble an agent to produce this. 



3. The increase of metamorphism would only have needed an increase in tem- 

 perature, and this may have been caused by the crumpling of the strata. 



4. Staurolite and fibrolite are widely distributed through the mica schists. 

 Evidently the metamorphism of the original rock — whatever its character — 



into a mica schist must have taken place at the time of its folding and crumpling. 

 Xow it is by no means certain that the forcible intrusion of a large body of 

 molten rock, far beloAv the surface, may not have exerted a pressure in accord- 

 ance with laws of hydrostatics sufficient to have caused the local puckering to be 

 seen at Cruger's. But this does not necessarily have any bearing on the ques- 

 tion. The original rock may have been crumpled and changed to a mica schist 

 by some orographic force, as Professor Dana thinks probable, and subsequently 

 have undergone a further contact-metamorphism by the agency of the Cortlandt 

 eruptives. The intrusion of the massive rock itself may have been — probably 

 was — the result of orographic movements. This intrusion may or may not have 

 caused the puckering, but the progressive metamorphism observed at Cruger's 

 bears such a direct relation to the contact line that the conclusion seems unavoid- 

 able that at least the mineralogical changes above described are directly due to 

 the influence of the eruptive rocks 



f Ou the Geological Relations of the Limestone Belts of Westchester County,. 

 N. T. This Journal. 1880 and 1881, vols, xx, xxi, xxii* 



% This Journal. Ill, xx, pp. 200-203 and 216, Sept., 1880. 



