GEOLOGY OF SARATOGA SPRINGS AND VICINITY 85 



The white weathering cherty beds. Associated with the black 

 shales of the Normanskill formation occurs a series of very hard, 

 splintery, dark to light greenish or black, cherty-looking beds 

 which weather with very light gray or white crust. These siliceous 

 beds frequently through their greater hardness, stand out as white 

 ridges and form characteristic landmarks. According to Dale 

 (o/>. cit., page i86) the white surface gives the reaction for 

 kaolinite^ and the rock was probably originally a feldspathic mud, 

 with quartz fragments and muscovite scales ; the latter two appear- 

 ing under the microscope as the principal constituents of the 

 cherty beds. 



The finding of Normanskill graptolites in the white beds at 

 several places on the Schuylerville sheet, notably in a small creek 

 just above Coveville and northeast of Willard mountain, leave no 

 doubt of the Normanskill age of the principal mass of the cherty 

 beds. There is, however, no doubt that similar cherty layers 

 occur also, though rarely, in the Snake Hill formation and that 

 all transitions occur from the common argillaceous shales through 

 slightly more siliceous and whitish weathering shales to the thick- 

 bedded, white-weathering cherty layers. 



On account of their great hardness the white beds most fre- 

 quently form the tops of ridges and can often be traced for some 

 distance along the strike of the folded beds. The more important 

 outcrops of white beds have been indicated on the map by the 

 blue symbols. These show that the principal areas of chert out- 

 crops are the region extending from Coveville northward to Thom- 

 son and Northumberland and that of the Willard mountain ridge 

 in the southeast corner of the quadrangle. In the former the 

 most striking chert ridge is seen i^ miles west of Victory Mills. 

 This forms cliffs seen from the Schuylerville branch of the Fitch- 

 burg Railroad, in which are solid beds of the cherty or siliceous 

 rock 30 feet and more thick. Other smaller ridges of white beds 

 protrude through the drift one-half of a mile west of Victory Mills 

 and on the water-swept plateau north of Coveville. Also south and 

 north of the Northumberland plug appear ledges of the harder 

 cherty beds on the hillsides and a small outcrop of very thick- 

 bedded, deep black chert was found just west of the entrance of 

 the Hudson river bridge at Thomson. 



^According to a later statement by the same author (1904, p. 36) the 

 weathering white of the chert may be due either to the loss of carbon or to 

 the kaolinization of a fine feldspathic cement. 



