84 



by my brother, not only upon specimens of the formation as it 

 occurs in Virginia, but upon other limestones of New York and 

 Kentucky, the details of which were submitted to the public in 

 his annual report on the geological survey of Virginia for the 

 year 1838. He there demonstrated that the magnesia is inva- 

 riably a prominent ingredient in all the limes which readily set 

 under water, while the other constituents, silica, oxide of iron, and 

 alumina, seem not to be essential, being variable, and most usually 

 existing in comparatively minute proportions. His researches 

 thus far made, would indicate that in the specimens yielding an 

 active hydraulic lime, the average proportion of the carbonate of 

 magnesia to the carbonate of lime is about three to five. 



In corroboration of these interesting and useful results, I here 

 present several analyses of the magnesian limestones of New 

 Jersey. After determining accurately the chemical composition 

 of each specimen, a portion of the same mass was carefully cal- 

 cined, made into cement, and left to repose under water, the pro- 

 gress and extent of the hardening being ascertained by an instru- 

 ment, devised by a French experimenter for that purpose. 



The more highly magnesian varieties proved in every instance 

 good hydraulic cements. 



Analyses. 

 Blue Limestone from Lafayette, Sussex county. 

 Description. — Colour, bluish gray ; texture, close-grained and 

 subcrystalline. 

 Specific gravity. — 2-838 at a temperature of 56° Fahr. 

 Composition. — In 100 parts: 



Carbonate of lime, - 53*04 



Carbonate of magnesia, - 41*04 

 Alumina and peroxide of iron, 0-96 » 



Insoluble matter, - 3-24 



Moisture and loss, - 1-72 



10000 



Blue Limestone, Johnsonburg, Warren county. 

 Description. — Colour, light bluish gray ; texture, slightly sub- 

 crystalline. 



