22 NEW YORK STATE MUSEUM 



valley, in the acute angle of the sharp turn which this stream makes 

 in the middle of the limestone-quartz-schist area, are some ledges 

 which show a somewhat unusual abundance of the mineral. Per- 

 haps the best development of tremolite, however, is to be found in 

 the northwestward- facing ledge on the west slope of the 460- foot 

 fiat-topped hill about one-half of a mile northeast of Pyrites railroad 

 track. It is likely that at either of these localities a little blasting 

 would loosen up material of good quality. 



A friable granular schist, composed almost wholly of a pale green 

 actinolite, is found associated with Grenville rusty gneisses in the 

 southern half of the small patch of Grenville undivided gneisses 

 in the extreme southeastern corner of the sheet. These sedi- 

 ments are closed in on three sides by granite gneiss, and on the 

 north are bordered by a narrow belt of crv'stalline limestone. The 

 two strata of actinolite schist, each probably not over 6 to 10 feet 

 thick, imdoubtedly represent layers of moditied limestone, acidified 

 perhaps by the invading magma which at this point is clearly in the 

 act of detaching a lenticular mass of Grenville material. So far as 

 the writer is aware, these two occurrences of actinolite rock are 

 unique on the Canton quadrangle. 



Another interesting but not very abundant variety of the limestone 

 formation is the serpentinous type or ophicalcite, which is best shown 

 in a led^e on the left bank of \'an Rensselaer creek, about one-fourth 

 of a mile north of the margin of the sheet. The serpentine is found 

 in isolated rounded lumps or bunches. As is shown by microscopic 

 evidence, the mineral is clearly of secondarv' origin; it is found in 

 circular, oval and irregular anastomosing spots of various sizes. 

 These show the serpentine to have originated at scattered points, 

 and to have enlarged itself at the expense of the calcite, which in the 

 latest stage of alteration is seen to be reduced to minute interstitial 

 patches. Such secondar}- clumps of serpentine may reach the size 

 of one's fist, and where they have resisted atmospheric disintegra- 

 tion may still retain glacial scratches or polish. Plate 2, lower 

 figure, shows the development of the serpentine and the residual 

 character of the peninsulalike fragments of calcite. 



The limestones are also obser^-ed in several places to grade 

 through increasing content of quartz into a type which may be des- 

 ignated as " quartz-mesh limestone." This is perhaps the most un- 

 usual phase of the limestone, though it appears on sufficient evidence 



