Williams — Contact-metamorphism, near Peekskill. 261 



the grain, shows layers of varying composition, all however 

 filled with metamorphic minerals. The original character of 

 the mica schist with muscovite, biotite and a little tourmaline 

 (cf. No. 21) is still well preserved, but the grain in the differ- 

 ent layers differs very much, and in some garnet, and in others 

 staurolite has been largely developed. 



1 . Inclusion of schist in mica-diorite showing concentric 

 arrangement of minerals. Length about five feet. 



A short distance beyond this point the schists give place to 

 the massive mica-diorite, when the inclusions become the ob- 

 ject of special interest. These show such a manifold variety 

 that hardly any two thin sections possess exactly the same min- 

 eral composition ; still all the specimens collected fall naturally 

 into four groups according to the nature of their prevailing 

 constituents, These groups are as follows : 



Group 1. Black inclusions consisting mostly of pleonaste 

 and corundum. 



Group 2. Inclusions consisting mostly of quartz grains. 



Group 3. Inclusions consisting mostly of staurolite and green 

 mica. 



Group 4. Inclusions consisting mostly of margarite. 



Group 1. The first inclusions encountered in following the 

 road up the hill side are the small black ones disseminated 

 through the mica-diorite. They are often arranged in rows 

 more or less sinuous, as figured in Professor Dana's paper.* 

 These are represented by Nos. 7, 7 a and 29 in the University 

 collection, and by W and Or. 7 in Professor Dana's. The micro- 

 scope shows them to be composed mainly of pleonaste in octa- 

 hedral crystals. With this is associated some magnetite, biotite 

 and feldspar. In the densest of the pleonaste inclusions, color- 

 less corundum is very abundant. This is notably the case in 

 No. 29, where this mineral forms comparatively large and well- 

 developed crystals. (PL YI, fig. 5.) 



These isolated inclusions of spinel and corundum are almost 

 identical with the more extensive deposits of the same charac- 

 ter occurring near the southern border of the norite region 



*Loc. cit., fig. 12. 



