1874.] 



95 



[Genth. 



Of the limestones only a few typical varieties have been more fully in- 

 vestigated, especially those from the Hostler and Pennsylvania Banks. 



Limestone at head op Hostler Bank. 



It has a fine crystalline granular structure and is mottled, whitish and 

 grey ; the surface is coated with ochreous argillaceous iron ore. 



A pure specimen from which the iron had been carefully removed, con- 

 tained : 



100.00 

 The atomic ratio between Magnesia and Lime is 1: 1.4, which is the 

 eomposition of some of the " pearlspar " varieties of dolomite. 



Limestone in Hostleb Bank. 



It lies four feet thick over 33 feet of pipeore. It has an ash-grey color 

 and a very fine grain, which is hardly perceptible to the naked eye ; very 

 friable. Its composition was found to be : 



0.24 Metallic Iron. 



^ 20.25 Magnesia. 

 = 29.02 Lime. 



100.00 

 The atomic ratio between Magnesia and Lime is 1: 1, which shows it to 

 be a true dolomite. 



Upper Limestone prom Pennsylvania Bank. 

 Dark grey compact, slightly crystalline 

 The analysis gave the following results : 

 Carbonate of Iron 



" " Manganese 



" " Magnesia 



" " Lime 



Quartz and Silicic Acid 

 Alumina 



100.00 

 The atomic ratio between magnesia and lime is 1 : 15. 



