148 NEW YORK STATE MUSfiUM 



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weather. For the glacier to leave a block of such shape in such 

 position in such a commanding situation is highly exceptional, and 

 it is one of the most striking objects of the kind that we have had 

 the privilege of becoming acquainted with. 



ECONOMIC GEOLOGY > 



BY H. P. GUSHING 



Molding sand. There is a large annual output of molding sand 

 from the general Hudson river region in New York, especially 

 from the vicinity of Albany. The Schuylerville quadrangle makes 

 a considerable contribution to this output, the material coming 

 from near the surface, just underneath the soil. The sand forms 

 part of the deposits of Lake Albany, which cover most of the sur- 

 face below the 300 foot level on the Schuylerville quadrangle. For 

 foundry purposes a sand must have a certain degree of refractori- 

 ness, cohesiveness, and porosity. Durability is also important, as 

 is texture, but sands of considerable difference in size of grain may 

 be used, the coarser for one kind of castings and the finer for 

 another. The cohesiveness results from the sand occurring mixed 

 with a certain percentage of clayey matter. 



The deposits of molding sand have no great thickness, running 

 from 8 or 9 inches up to a few feet thick. They commonly pass 

 into worthless sand below. Good natural molding sands are not 

 very common, so that the demand rather exceeds the supply. 



Graphite. Mining for graphite has been carried on at two dif 

 ferent localities on the Saratoga quadrangle, both of them quite 

 recent projects. The older and larger of the two establishments 

 is situated about 2 miles west of Porter Corners on the fault plane 

 scarp of the Hoffmans fault. The other is 4 miles north of Sara- 

 toga , Springs, and similarly situated on the McGregor fault plane 

 scarp. The rock is quite similar at the two localities and seems 

 to represent the same horizon in the Grenville series, a horizon in 

 the quartzite formation. At the time of our study only the estab- 

 lishment at Porter Corners, the Empire Graphite Company, was 

 in operation. 



The Grenville beds at this locality have a N'. 70° E. strike and a 

 dip of from 30° to 50° to the south. The surface beds are soft 

 and badly altered graphite and mica schists. They are quartz- 

 feldspar-graphite and quartz-feldspar-phlogopite rocks, averaging 

 50 per cent quartz, 30 to 40 per cent of feldspar and the remainder 



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