NOTES ON THE MICROSCOPIC STRUCTURE 36 1 



acicular crystals (undetermined). The muscovite and bio- 

 tite are both fresh in appearance. The biotite is only an 

 occasional mineral. 



Sandstone, Potsdam Red Sandstone Company, Potsdam, St. 

 Lawrence County.— Consists almost exclusively of quartz. 

 The grains are subangular and quite clear. The cloudiness 

 is due to minute crystals and to pores filled with either gas 

 or fluid of some kind. Many of the grains show a second- 

 ary enlargement. The growth is indicated by a clearer rim 

 of quartz, separated from the inner core by a ferruginous 

 rim. The cementing material is almost wholly silica. The 

 interstices are filled with a cloudy mass, apparently fine 

 grains, cemented, as the larger ones, by silica. 



Blue-stone, Bigelow Blue Stone Company, Maiden, Ulster 

 County.— Minerals : quartz and feldspar. The quartz is in 

 grains which appear to be very angular in shape, more like 

 a breccia. And the grains are clearer than those of the 

 other sandstones examined. And the proportion of quartz 

 grains to the rest of the matter is smaller. The feldspars 

 observed differ very materially from that in the other stone, 

 Several grains of a triclinic feldspar were observed, which 

 were very fresh. ' Another feldspar is almost completely de- 

 composed. No carbonate of lime appears to be present, 

 and very little oxide of iron. The long, wavy, crystal-like 

 dark spots in the stone appear to be decomposed feldspar, 

 more or less stained with iron. The cementing material is 

 probably silica, as dilute hydrochloric acid has no effect, and 

 is not stained with iron. 



Sandstone, Oxford Blue Stone Company, Oxford, Chenango 

 County. — Much like the preceding. 



Sandstone, Hughes Brothers, Oswego Falls. — Component 

 minerals : quartz and feldspar. The quartz is in angular 

 grains, and has fluid cavities with bubbles. The more nu- 

 merous cavities are too small to distinguish the filling mat- 

 ter. Acicular crystals are rarely present. The feldspars 

 are wholly kaolinized, often dirty and discolored from the 

 46 



