324 C. H. GORDON 



tive character of the rocks is found in the inclosures of country 

 rock sometimes observed in them (Figs. 2 and 3). An occurrence of 

 this kind at High Rock is noted in the above-cited report by Pro- 

 fessor Penrose whose figure is here reproduced. 



The evidence, therefore, clearly warrants the conclusion that the 

 pyroxenic rock is intrusive. And that it represents the oldest intru- 

 sive is shown by the manner in wdiich it is cut by the later intru- 

 sions of syenite and diorite, or so-called "trap." 



NOMENCLATURE. 



As heretofore stated, the term "pyroxenite" was first used by 

 Dr. Hunt for an intrusive rock composed mostly of pyroxene with 

 magnetite and ilmenite from Mount Royal and other places in Can- 

 ada.' Later^ he applied the name to the pyroxenic member inter- 

 calated in the limestones and quartzites of the apatite district, a 

 rock generally regarded as having no genetic relationship with the 

 first. Among the Canadian geologists it has come to be applied 

 almost exclusively to the latter rock. Lacroix uses the term gneiss 

 a pyroxene et a wernerite for a rock of essentially the same character 

 from Brittany. 3 In the later work'* Lacroix conforms to the German 

 and English usage of calling this rock an "augite gneiss." These 

 gneisses are said to occur in the upper part of the gneiss system, 

 and are usually characterized by scapolite in greater or less abund- 

 ance as in the Canadian rocks. The term "pyroxenite," which had 

 previously been applied to these occurrences, is reserved by this 

 author for rocks composed exclusively of pyroxene. 



In 189G G. H. Williams^ used Hunt's term in its original sig- 

 nification for basic intrusions occurring in the eastern portion of the 

 Piedmont Plateau in Maryland. These- rocks are of a somewhat 

 different type from the Canadian rocks, in that they are composed 

 chiefly of an orthorhombic instead of a monoclinic pyroxene. Wil- 

 liams speaks approvingly of Lacroix's substitution of the term 



^ Geology of Canada, 1863, p. 667. 



^Catalogue oj Canadian Rocks at Paris Exposition, 1862; Geology of Canada, 

 1863-66, pp. 185-226. 



3 Bulletin de la Societe frangaise de Mineralogie, Vol. X (1887), p. 288. 



■• Ibid., Vol. XII (1S89), p. 83. 5 American Geologist, Vol. VI (1890), p. 35. 



