Fig. ii Potsdam sandstone, East ' Dickinson Moira, Franklin county. 

 Taken with nicols crossed, magnification 65 diameters. Composed almost 

 wholly of quartz ; the original rounded grains have been enlarged by second- 

 ary growth and are fairly free from included matter. Most of the impurities 

 (chiefly sericite and a little iron oxide) have an interstitial distribution, 

 and may be in part removed by washing the crushed rock. 



