GEOLOGY OF FRANKLIN COUNTY 93 



white pyroxene, and it is by the alteration to serpentine of the 

 latter mineral that the ophicalcites of the series are produced, as 

 was long ago shown by Merrill. 1 These beds of limestone vary 

 much in thickness in different places, but no evidence has been, 

 forthcoming in Franklin county to throw any light on the number 

 of limestone beds or the possible thickness of the series. 



Beds of pure limestone have been noted at only two localities in 

 the county, at Franklin Falls and in the southern part of Malone 

 township. At the old kiln near the Saranac river, 2 miles below 

 Franklin Falls a massive bed outcrops, which is exposed for 100 

 yards across the strike, denoting a thickness of at least 150 feet 

 if the dip is continuous throughout. As their outer surfaces are- 

 approached, the limestones become very impure, containing great 

 quantities of green pyroxene and much quartz, with often scapo- 

 lite and white pyroxene as well. Precisely similar beds are often 

 found inclosed in gneisses and wholly apart from any large lime- 

 stone bed. Good exposures of such are found by the roadside one 

 half mile north of the bridge at Franklin Falls (see pi. 5). They 

 weather rapidly on account of the leaching out of the calcite, and 

 are among the most characteristic rocks of the series. 



Quartzites have not been noted in Franklin county. Very- 

 quartzose gneisses occur which hold invariably a respectable per- 

 centage of orthoclase. An evenly granular, rapidly disintegrat- 

 ing, white gneiss which usually contains much graphite and con- 

 sists essentially of quartz and white pyroxene, of ten with consider- 

 able pyrite, is a very common rock in this county, associated with 

 the limestones, and is a decisive indication of the presence of the 

 series in places where the limestones are lacking. Scapolite is a 

 quite common mineral near contacts, and some of the quartz- 

 white-pyroxene gneisses hold abundant scapolite. Graphite is a 

 very important mineral in the diagnosis of this series, occurring in 

 many of the gneisses as well as in the limestone. But some care- 

 is necessary in localities where exposures are meager, since this 

 mineral also is found sparingly in some of the more acid igneous 

 rocks. Sillimanite is another quite characteristic mineral, 



lMerrill, G. P. Amer. jour. sci. Mar. 1889. 37: 189-91. 



