122 The Limestones, and Lime. [March, 



The first occurs at Rockland furnace, Venango county. Color 

 grayish drab; compact, and fine grained. 



The second occurs at Sugar creek, Armstrong county. Color 

 blueish gray; mostly compact. 



In Virginia, many beds of limestone appear, which belong to 

 the lower part of the New-York system, which have been em- 

 ployed as cement. 



The two following analyses are abstracted from the Report of 

 Wm. B. Rodgers: — 



Carbonate of lime, 

 Carbonate of magnesia, 

 Alumina and oxide of iron, 

 Silica and insoluble matter, 

 Water, - - - - 

 Loss, ... 



The first occurs at or near Sheppardstown, on the Potomac, 

 Va. The second at the Natural Bridge, and Cedar creek. Both 

 are said to make a good hydraulic cement. 



Dr. Jackson, in his Maine Report, gives the analysis of an 

 hydraulic limestone, which is found at Machias, upon Starboard's 

 creek, which we subjoin: — 



Carbonate of lime, - - - - 59.5 



Carbonate of iron, .... 6.0 



Silica, 14.0 



Alumina, ...... 15.0 



Oxide of manganese, ... 4.0 



Water, 1.5 



100.00 



The geological position of this limestone is doubtful. We 

 have supposed that it might be referred to the New Red Sandstone 

 period. W^e notice this hydraulic limestone, for the purpose of 

 showing that magnesia is not essential to give lime the property 

 of hardening under water. This indeed had been shown by 

 Jackson's analysis of Parker's celebrated cement, which we here 

 .subjoin; and with which we shall close this part of the subject 

 relating to the composition of limestones in the United States. 



