THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE 4I 



calcareous laminae of more pronounced sedimentary aspect and, be- 

 tween them, all gradations and transitions can be observed. The 

 new cuts along the recently constructed (1912) state road from 

 Canton to Eddy, afforded many typical exposures for the examin- 

 ation of these micaceous rocks. The frequent rusty color of the 

 surface, which varies considerably in intensity, betrays the presence 

 of pyrite, often in notable amount; less abundantly but quite con- 

 stantly can tiny flakes of graphite be observed throughout this gen- 

 eral district. 



In the southern portion of the area mapped as Grenville undi- 

 vided gneisses, the rapid disintegration (see plate 7, lower figure) 

 and partial discoloration of the sediments can be traced to a further 

 cause, namely, the presence of calcite, sometimes as an interstitial 

 cement in the quartzose or silicate beds, more often as thin, coarsely 

 crystalline layers intimately interbedded with them. 



The presence of calcite, both in thin laminae and as fairly mas- 

 sive limestone strata often 12 to 15 feet thick, indicates a marked 

 difference in the conditions of sedimentation as compared with the 

 area immediately west and southwest of Canton; but the larger 

 structural features in this part of the country are so obscure that it 

 can not be definitely ascertained whether the change is to be consid- 

 ered as lateral or vertical. However, the prevailing southwesterly 

 pitch of the folds suggests a later age for the calcite-bearing series, 

 and consequently a deepening of the basin of deposition may be as- 

 sumed. But the whole problem is veiled in great uncertainty, and 

 even if a marine transgression be admitted, there is no dependable 

 method for determining the direction of strand-line movement. 



Included for the sake of simplicity with these calcareous and 

 gametiferous mica schists in the areas mapped as undivided gneisses 

 are occasional patches of rock of somewhat nondescript character, 

 but undoubtedly of Grenville affinities. The microscope generally 

 reveals these to be alterations or varieties of the more usual types, 

 chloritic or serpentinous, fine-grained, hematite-stained products 

 being the most common. Such rocks, which are unimportant from 

 an areal or systematic point of view, may be found at the mouth 

 of the reentrant northeast of Pyrites, and on the southeast bank of 

 the Little River flats about half w-ay between the fork in the Canton- 

 Russell road and the right-angle turn in the course of the Grass 

 river. 



A few^ remaining occurrences of undivided gneisses are found 

 in the southern part of the sheet in small isolated areas. In 

 some cases these were caught up as xenoliths in the basic magma ; 

 in others, as midway between Pyrites and North Russell, they are 



