62 XEW YORK STATE MUSE CM 



metamorphic amphibolite of the Pierrepont sigmoid, and because of 

 the possibihty that an indefinite proportion of this hornblende may 

 have been primar\- in the intrusive, the generahzed term, gabbro- 

 diorite, would seem to be the more satisfactory- designation to apply 

 to these rocks. 



On going westward and northward from this vicinity, the rock 

 assumes a gneissoid and finally a strongly schistose structure, with 

 a concomitant alteration of all its pyroxene into amphibole and 

 liberation of free silica, and the production of true hornblende schist 

 or amphibolite. These altered equivalents of the gabbro-diorite may 

 be traced continuously southwestward into the vicinit}- of the Stella 

 pyrite mines, near Hermon ; and northeastward as far as Boyden 

 brook, just beyond Waterman hill; farther than this they are lost 

 under the drift. There is therefore small difficulty in the way of 

 establishing these schists as of metamorphic igneous origin. 



That the gabbro-diorite and its derived schists are intrusive into 

 the Grenville and not the basement upon which these sediments 

 were laid down is. moreover, conclusively demonstrated by the 

 numerous xenoliths of limestone, quartzite, gametiferous and py- 

 ritiferous gneisses scattered irregularly in the amphibolite between 

 Pyrites village and Harrison creek. Twelve such inclusions were 

 noted, rive of limestone,, three of pyritous gneiss, one composed of 

 both these t}-pes, one of thin-bedded quartz-schist, one of biotitic 

 and locally gametiferous gneiss, and one of impure weathered 

 schist of ill-defined character. On account of the heavy cover of 

 glacial delta material which is spread over a large part of this gab- 

 broid area, the detailed relationships of some of these masses can 

 not be made out with certainty and their xenolithic character is in- 

 ferred ; but with others their inclosure within the basic rock is be- 

 vond question. The Hmestone xenoliths are of white, coarse-grained 

 material, with or without irregular development of actinolitic or 

 serpentinous blotches, all apparently identical with various phases 

 of the limestone which occur in the main body of the Grenville. 

 The pvritous gneisses are lithologically like that already described 

 in the Pvrites gorge : but the structural relations are not so well 

 shown. The smallest patch is not seen in contact with the amphibo- 

 Hte. while the long strip along the southern edge of the intrusive 

 area is apparently in the act of being ripped ott the wall of the 

 magmatic chamber and being inclosed within the gabbro-diorite. 



