Williams — Contact metamorphism near Peeksktll. 267 



Near the foot of Broadway in Verplanck the limestone frag- 

 ments occur imbedded in the norite as figured by Professor 

 Dana,* while just behind and beyond the hotel branching 

 dykes of the massive rocks, varying from a fraction of an inch 

 to many yards in width, penetrate the limestone in different 

 directions, though in the main they follow the direction of its 

 bedding. The microscope shows that these dykes belong to 

 many different rock types, as for instance gabbro (Nos. 109, 

 111), mica-hornblende-diorite (No. 80), hornblende-diorite {Nos. 

 82 and 83) and mica-diorite (No. 81). 



The metamorphic action extends but a small distance from 

 the actual contact, but is always unmistakable in its nature. 

 The limestone is in almost all cases bleached and is frequently 

 rendered more coarsely crystalline. There are new contact- 

 minerals developed in it, among the most common of which 

 are hornblende and pyroxene, both rich in lime and of a pale 

 color. * 



In the narrowest dykes, the nature of the eruptive rock is 

 also considerably modified. In one of these (No. 77), the 

 entire width of the dyke (only one-eighth of an inch) is con- 

 tained within the thin-section. The intrusive material consists 

 of brown hornblende, biotite, triclinic feldspar, apatite and an 

 abundance of a brightly polarizing, uniaxial, negative, colorless 

 mineral, which is probably scapolite. The brown hornblende 

 is concentrated along the edges of the dyke and often stands 

 perpendicular to its walls. The limestone beside the eruptive 

 material is highly crystalline and contains colorless pyroxene 

 and muscovite. 



In some cases, as for instance in a section of Professor Dana's 

 collection, the metamorphic action is extremely slight even 

 when seen under the microscope. This particular section con- 

 tains the contact between a mica-hornblende-diorite and lime- 

 stone. The only change in the former is a concentration of 

 hornblende along the contact line, while the limestone has 

 become slightly more crystalline and contains oval spots of ser- 

 pentine. 



In the cutting exposed on the West Shore Railroad at Stony 

 Point, a narrow band of limestone is seen between the masses 

 of mica-diorite and peridotite, which, but for this, come here 

 in contact. This limestone is very crystalline and is filled 

 with minerals doubtless derived from the eruptive rocks. 

 There is a pale pyroxene (malacolite), a light green hornblende, 

 zoisite, sphene, and quite abundant scapolite. 



At the conclusion of this series of papers, it may be advis- 

 able to summarize the evidence in favor of the eruptive (igneous) 



* This Journal, III, xx, p. 202, fig. 5. 



