THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE 63 



The largest of the xenoHths is a long strip of micaceous gneiss from 

 15 to 50 feet thick, traceable along the left bank of the Pyrites 

 gorge southward from the middle intersection of the river bed with 

 the ore body, and thence southwestward nearly to the south border 

 of the amphibolite area. In the gorge this formation lies above 

 the ore body, though separated from it by 30 to 50 feet of gabbroic 

 material, and the two xenoliths are parallel for several hundred feet. 

 Though these have this much in common, any opinion as to whether 

 they were originally joined along a common bedding plane, and 

 have been pulled apart by movements in the viscous magma and 

 separated by the introduction of basic material, can not fail to be in 

 the highest degree hypothetical. 



Along the west edge of the gorge and at the jog in the northwest- 

 southeast road nearby, excellent exposures show the micaceous 

 gneiss to be considerably sheared and more or less admixed with 

 gabbroic material, as though the xenolith were in the process of 

 being partially absorbed by the magma. So far as observed this 

 is the only point where any of the xenoliths in the gabbroid intru- 

 sive can be said to be affected by contact action; and even here, 

 unless the phenomena are misinterpreted, the action is one of mar- 

 ginal injection and absorption of an already metamorphosed rock 

 rather than contact alteration of the more usual type. The most 

 notable feature of these xenoliths is the general lack of meta- 

 morphism directly and unquestionably attributable to the immediate 

 influence of the gabbro-diorite magma, and this point is readily seen 

 to substantiate the impression obtained from an independent study 

 of the Pyrites ore body. In other words, either the basic intrusive 

 as a whole was incapable of producing special alterations in an 

 already thoroughly and independently recrystallized Grenville suc- 

 cession, or else it produced or completed a kind of regional meta- 

 morphism in wdiich the individuahty of the various Grenville units 

 was preserved and reflected in the end-products. 



From the data given on the foregoing pages, it appears that in 

 two separate places on the Canton sheet, Pierrepont and Pyrites, 

 are there basic intrusives cutting and including portions of the Gren- 

 ville sediments. The continuity of these igneous masses would be 

 an interesting relationship if it could be established. The forma- 

 tions, however, are not visibly connected with one another, but at 

 the point where they should join they are covered by a heavy 



