50 ANNALS NEW YORK ACADEMY OF SCIENCES 



typical mesh-structure, though most of it has neither the antigorite nor 

 the bastite habit. It most resembles the former, however, and a hypers- 

 thenite dike so completely altered would be a curiosity. There is also a 

 small amount of sericite, quartz and biotite. In the other cases, the 

 typical antigorite or mesh-structure, indicating the former presence of 

 olivine, permeates the whole rock. Traces of altered white augite are 

 still visible; but the rock was evidently almost entirely olivine. In all 

 three cases, a considerable amount of magnetite is present. 



ABNORMAL CONTACT ROCKS 



The true igneous character of the series is proved by the frequent 

 presence of contact action. This usually occurs along its borders, but 

 several very peculiar and abnormal developments are to be found within 

 the area itself which can only be explained by considering them as due to 

 the contact action on the inclusions which are fairly common in the 

 western part of the area. 



Williams 34 has given such a minute description of what seems to be the 

 characteristic type of border contact action that it would be superfluous 

 to describe in detail the work which the writer has done along the same 

 line. The general result seems always to be that the mica schist increases 

 in alumina content as the massive rocks are approached; and this is 

 attended by the formation of such aluminous minerals as staurolite, 

 sillimanite, cyanite and garnet. A very striking feature, and one whose 

 importance will be emphasized later, is the great increase in the amount 

 of biotite, which at a point ten yards from the contact at Crugers consti- 

 tutes the bulk of the schist; and magnetite is thickly scattered through 

 the mica. Contained in the diorite itself at this point are numerous small 

 schist inclusions, and these in like manner furnish excellent opportunity 

 for the study of contact action. They are largely changed to pleonaste 

 and corundum in some cases ; in others to quartz ; in others to staurolite 

 and green mica. The first case resembles the emery from the mines very 

 closely. 



Along the limestone contact, which exists only on Stony Point and at 

 Verplanck, contact action of a different kind has taken place. The com- 

 mon minerals developed are usually pale green amphibole and pyroxene ; 

 more rarely titanite, zoisite and scapolite are formed (these last were 

 observed on Stony Point). Similar effects have been recorded by Kemp 

 from the Rosetown area, 35 where the limestone contact is especially well 

 shown. 



M Amer. Jour. Sci., (3), XXXVI, 254. 1888. 

 * Op. cit., p. 252. 



