GEOLOGY OF SARATOGA SPRINGS AND VICINITY I49 



a varying mixture of graphite and phlogopite with some apatite. 

 The feldspars are so badly altered as to defy exact determination, 

 but in part at least consist of plagioclase, likely oligoclase. Two 

 beds are being utilized, or are capable of utilization, because of 

 high graphite and low mica content. The upper bed, from lo to 

 14 feet thick, has been the one chiefly worked up to date. The 

 lower bed is much thinner. They are separated by a four- 

 foot thickness of quartzite and thin limestone. Underneath is a 

 much more solid bed of mica gneiss. The whole overlies massive 

 quartzite and, like all the Grenville of the quadrangle, is more or 

 less involved with the white, garnet-bearing granite which we re- 

 gard as Laurentian. There has been an irregular output of graphite 

 by this company since 1906, the production being exclusively flake 

 graphite. 



Much the same assemblage of rocks is shown at the pit of the 

 Saratoga Graphite Company, but this is a newer enterprise with 

 much less accomplished in the way of exploitation. Similar weak, 

 altered schists are shown, of the same mineralogic make-up as at 

 Porter Corners. We saw no rock so free from mica as are the 

 two beds worked by the Empire company, though further explo- 

 ration may disclose equally good material. The strike here is 

 N 80° E, and 30° south dip, and the general similarity of the rock 

 association strongly suggests that we are dealing with the same 

 rock horizon. 



Stone quarries. Quarries have been opened in several of the 

 formations of the two quadrangles, in the Precambric granite and 

 trap, in the Little Falls dolomite, the Amsterdam limestone, the 

 Bald Mountain limestone, and the Northumberland volcanic plug. 



Laurentian granite. A small quarry has been opened in the 

 Laurentian white granite on the face of the McGregor fault plane 

 scarp, 2 miles north of Saratoga. Like all the granite of the dis- 

 trict it contains Grenville material in all stages of absorption. But 

 the quantity of such inclusions of schist is much less here than 

 elsewhere, the granite is massive and solid and of pleasing color, 

 and there seems no reason why it should not make a most excel- 

 lent structural material for many purposes. The location, how- 

 ever, is unfortunate, the quarry being situated well up the steep 

 slope of the fault plane scarp, rendering cartage difficult and 

 expensive. 



Trap. A large quarry has been opened on one of the large 

 diabase dikes where it is crossed by the North Creek branch of 



