EIvISHA MITCHELL SCIENTIFIC SOCIETY. 27 



the olivine-actinolite variety, has been observed only in 

 connection with dunite, thoug-h some chloritic olivine 

 rocks are doubtless altered forms of this variety. Troc- 

 tolite (forellenstein) consists essentially of olivine and 

 anorthite, with zones of intermediate fibrous minerals 

 always separating- them, and sometimes also bears 

 larg-e dark hornblende. By gradual transition it pass- 

 es, on the one hand, into dunite, and, on the other, in- 

 to the feldspar type aiiorthosite. 



The Pyroxenites, — This class is represented by two 

 types, which seem to be quite distinct, as no transitional 

 forms have yet been found. Enstatite-rock, as the 

 name indicates, is composed of orthorhombic pyrox- 

 ene, and seldom contains any other mineral in prom- 

 inent proportions. It often occurs in small masses with 

 dunite and harzburg-ite, thouo-h considerable outcrops 

 in some localities are composed of it entirely. In some 

 of these instances there is apparently evidence of its 

 origin from peridotites. Websterite, the enstatite-di- 

 opside type, is found in the midst of the peridotites 

 about Webster, Jackson count^s North Carolina. This 

 type was first recognized and described by the late 

 Dr. G. H. Williams," and similar rocks were studied 

 from Baltimore county, Maryland, where transitional 

 forms were found connecting it with peridotites, bron- 

 zitite, gabbros, and norite. At the Webster locality, 

 however, no such intermediate types have been ob- 

 served. 



Aynfhibolite. — Only one type of this class has been 

 found in the peridotite belt. It is composed of a bril- 

 liant, grass-green, aluminous amphibole, which often 

 bears considerable anorthite and is only occasionally 



* Am. Geologist, VI, 1890, 40-49. 



