SOME AMERICAN DOLOMITES 



BURLEIGH B. REED AND NICHOLAS KNIGHT 



These rocks are among the important building materials of the 

 country and have a wide distribution. We secured a few typical 

 specimens from different sections, in order to make a comparison 

 of their chemical composition. The specimens analyzed are all used 

 as building stones in their respective localities. 



1. This is a specimen from Mount Vernon, Iowa, and represents 

 the Niagara formation, the oldest member of the Silurian age. It 

 is of a yellowish gray color, due to the presence of iron. The sub- 

 stances which compose the rock are as follows : 



Per Cent 



SiOo 1-29 



Fe.>6.{ and AI..O3 0.57 



CaC63 55.17 



MgCdg 43.04 



Total 100.07 



2. This is a specimen of dolomite from West Chester county. 

 New York, not far from New York City. It is a white crystalline 

 rock, resembling marble. The formation is a part of the Cambro- 

 Silurian and is believed to be equivalent to the Stockbridge lime- 

 stones of the Housatonic Valley in Massachusetts. It is quite a 

 typical dolomite in composition, not materially different from the 



Iowa rock. The analysis is as follows : 



Per Cent 



Si02 2/71 



FegOg and AL.Os 105 



CaCOg '. 53.43 



MgCOg 42.93 



Total 100.12 



3. A specimen was obtained from Lockport, New York, also 

 belonging to the Niagara Limestone. There was upon the dark- 

 gray limestone an incrustation of milk-white crystals, and the 

 composition of these also was determined. The analysis of the 



gray body of the rock resulted as follows : 



Per Cent 



Si02 2.76 



FeoO^ and AI0O3 1-42 



CaCOa 51.85 



MgCOs 43.94 



Total 99-97 



