1 6 NEW YORK STATE MUSEUM 



In these various localities the rock is a friable to fairly compact, 

 granular, quartz sandrock, rather thin bedded, and dipping at a 

 small angle (7 to 10 degrees) in a northerly to northwesterly 

 direction. 



The maximum thickness of individual beds is from 6 to 8 inches ; 

 many of them are more or less iron stained and apparently not 

 sufficiently pure for use in the manufacture of glass, but some are 

 white and quite pure. Analyses of the better beds (table i ; Pots- 

 dam, Moira-Bangor) gave 99.22 per cent SiO 2 and 98.99 per cent 

 SiO 2 respectively; an analysis of one of the less pure beds gave 

 95.08 per cent SiO 2 (no. 3). 



In the latter case (no. 3), sericite is the chief impurity, as shown 

 by the high alumina content (3.27 per cent) and in the photomicro- 

 graph (figure 13). It should therefore be possible to improve the 

 quality of material of this grade by washing; an analysis of the 

 crushed and washed rock (table 2) shows an increase in silica, 

 from 95.08 to 97.46 per cent, and a decrease in iron oxide from 

 0.24 to 0.15 per cent. Samples from beds of better quality (no. I 

 and no. 2) show likewise an increase in silica, when crushed and 

 washed; no. i, from 99.22 per cent SiO 2 to 99.54 per cent, and 

 no. 2 from 98.99 to 99.33 per cent. The better beds of this forma- 

 tion in the localities mentioned seem to offer, therefore, possibilities 

 as sources of supply for glass-making rock, so far as indicated by 

 these analyses. 



Potsdam outliers in the Mohawk valley. Ten or 12 miles west 

 of Johnstown, in Fulton county, an outlier of Potsdam sandstone 

 occurs, which resembles in lithologic character the rock in the Moira- 

 Bangor area; promising rock also lies near Yosts Station, on the 

 New York Central and Hudson River Railroad, in Montgomery 

 county, probably a part of the same outlier. The rock in Fulton 

 county is more massively bedded than that on the northern edge of 

 the Adirondacks in Franklin and Clinton counties, but it is similar 

 in other respects. It is a massive, rather heavily bedded, moderately 

 granular, friable to compact, fairly pure, quartz sandrock, generally 

 white, but more or less variable in color and purity ; some beds are 

 flecked and streaked with iron oxide, but the chief impurities are 

 sericitic and kaolinitic matters derived from altered feldspar grains. 



The best material carries 98.84 per cent SiO 2 , the poorer beds 

 96.83 per cent (table i) ; washing the crushed rock increased the 

 silica contents to 99.05 and 97.46 per cent respectively (table 2). 



Quartzite phase of the Potsdam. In some localities the Pots- 

 dam is a typical quartzite, which in general, and in most places, 



