150 NEW YORK STATE MUSEUM 



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the railroad, 2 miles north of Saratoga. This dike is at least lob 

 feet wide on the average, and seems a very long one. Its average 

 trend is N 20° E to N 25° E. For three quarters of a mile south 

 of the quarry it can be followed unbroken, and north of the quarry 

 we have picked it up so repeatedly when crossing its probable 

 location as to convince ourselves that it must be the same dike 

 throughout. 



The rock is an ordinary diabase, an augite- feldspar-magnetite 

 combination, lacking olivine. It shows everywhere considerable 

 alteration, the feldspars much kaolinized and the augite largely 

 changed to chlorite. These changes do not seem, however, .to have 

 seriously impaired the strength and toughness of the rock and 

 should not, in our opinion, much impair its value as a road rock, 

 for which purpose it has been chiefly used. Because of its width 

 and great length this dike is capable of furnishing a large supply 

 of road material. Where worked it is at low altitude and adjacent 

 to a railroad. Its northern extension is less fortunately situated 

 in these respects, and the same is true of the other dikes of trap 

 in the Precambric. But since the demand for good trap for road- 

 making purposes in New York at the present time is large, and 

 the supply from the dikes in the Adirondack Precambric is the 

 only available source in the State outside of Rockland county, it 

 would seem as if there was opportunity for some development 

 of the industry in the Saratoga region, owing to the unusual 

 length and width of the dikes. 



Dolomite. Two quarries have been opened in the upper beds of 

 the Little Falls dolomite, within the limits of the two quadrangles, 

 one on Maple avenue in the northern edge of Saratoga Springs, 

 and the other a mile south of Wilton, Schuylerville quadrangle. 

 In both cases the quarries are in the upper, light colored, coarsely 

 crystalline beds of the formation. In the Maple avenue quarry 

 a thickness of 22 feet of massive beds is exposed with a dip of 

 about 5° to the southeast. The upper bed is full of chert; some 

 of the lower beds are full of drusy cavities lined with dolomite 

 crystals and containing crystals of clear, transparent quartz. A 

 small fault is well shown in the quarry wall which is of interest 

 because it seems very old. The throw is only 2 feet, but a strip 

 of fault breccia about 6 inches wide was produced, which was 

 subsequently solidly welded up by deposit of calcite from cir- 

 culating waters, so that the rock is as strong and firm as it is any- 

 where in the quarry. The quarry is worked only intermittently. 



