THE MINING AND QUARRY INDUSTRY 145 



as to give a special character to the grains, we speak of this feature 

 according to the prevailing mineral, as feldspathic, calcareous, mica- 

 ceous etc. According to the principal cementing material sand- 

 stones may be designated as silicious w^hen the cementing material 

 is silica, calcareous when it is calcite, ferruginous when it is an 

 oxid of iron, and argillaceous when the cement is some form of clay. 



In chemical analysis the grains and cementing material are usually 

 treated as a whole ; the estimation of silica for example includes the 

 amount of quartz present in both these forms, as well as the silica 

 found in the feldspar and any other minerals which the rock may 

 contain. Accordingly the analysis does not always show the true 

 amount of free silica or quartz present, but this may be obtained by 

 recasting the analysis. 



In color sandstones are to a greater degree dependent on the 

 character of the cementing material than on that of the grains. 

 The color may range from a nearly pure white, in rocks where the 

 cementing material is silica, to various shades of red, brown, olive- 

 green, purple etc. The greatest range of color is afforded by those 

 with ferruginous cements. Permanency of color is also affected 

 by the nature of the cementing material. Those compounds in 

 which iron is present in the higher stage of oxidation are more 

 durable than compounds with the lower or ferrous oxid. 



The weight of a certain volume of sandstone is dependent upon 

 the character of the minerals composing the rock and the state of 

 aggregation of the component parts. If the space between the 

 grain is well filled with cementing material, the rock will be more 

 dense in proportion to the amount of pore space filled. The 

 apparent weight of the stone is increased by the amount of water 

 absorbed, which in volume is from one third to one half of the total 

 amount of pore space. A dense quartzite may weigh as much as 

 170 pounds a cubic foot, giving the rock a specific gravity above 

 pure silica. The average range in weight of sandstones is 135 to 

 165 pHDunds a cubic foot. 



The distribution of sandstones in New York, with a brief descrip- 

 tion of their character, economic value, etc. is given herewith. 



Potsdam sandstone. This sandstone belongs to the Upper Cam- 

 bric and is the lowest formation which is utilized in New York State 

 for building purposes. The most extensive outcrops of the Pots- 

 dam are along the northwestern and northern border of the Adiron- 

 dacks, in Jefferson, St Lawrence, Franklin and Clinton counties. 

 Other important outcrops though of much less area than the above 

 are found along the eastern and southeastern border of the Adiron- 



