38 New York State Museum 



character is present. Lithographic stone is a very pure 

 lime mudrock or limestone, so fine that organic remains 

 are preserved in it with wonderful perfection. Bitumi- 

 nous limestones are dark rocks which when broken or 

 struck give off a strong bituminous odor. When the rock 

 is more or less filled with green grains of glauconite it is 

 termed glauconitic limestone. Some limestones show a 

 great abundance of fossils and according to their fossil 

 content are shell limestones, crinoidal limestones etc. 

 Limestones are fine-grained to very dense in texture and 

 show a variety of colors — white, yellowish to brown, 

 various shades of gray to black. Reddish colors are rare. 

 Reddish and yellowish tinting or blotching is often seen 

 on exposed surfaces where the iron carbonate constitu- 

 ent has become oxidized. Iron oxides give the yellow 

 and brown colors to limestone, organic matter the gray 

 and black colors. Limestones are generally distributed 

 throughout the world. They are used for structural pur- 

 poses, in the manufacture of quicklime, Portland cement, 

 as a flux in smelting operations etc. 



Dolomite is not an original rock, but is formed as a 

 transition from pure limestone through the substitution 

 of magnesia for part of the lime by waters holding mag- 

 nesium salts in solution or from impure (dolomitic) lime- 

 stone by solution of the lime and consequent concentra- 

 tion of the magnesia content. A dolomite geologically is 

 a rock consisting dominantly of a carbonate of calcium 

 and magnesium, but there may be an admixture of cal- 

 cite (calcium carbonate). It is like limestone in appear- 

 ance but is harder and if pure will react but very slowly 

 to cold hydrochloric acid. The chemical test for mag- 

 nesia is the best test. The occurrence of dolomites is 

 much the same as for limestones. Oolitic limestones and 



