Western district. 275 



The above analysis represents the composition of the western hydraulic limestone. The 

 same series exist, however, in Ulster county. Their analysis was made by Dr. Jackson, 

 and gave the following result : 



Water 1-182 



Silicic acid 10-087 



Carbonic acid 41- 200 



Sulphuric acid 0-606 



Lime 25-087 



Alumina 3 -395 



Peroxide of iron 3-274 



Magnesia 12 - 890 



Oxide of manganese 0-606 



Potash 0-700 



Soda 2-182 



100-000 



One hundred grains of the powdered rock give one grain of soluble matter ; of which 

 there remains after ignition, 0'56 of a grain, leaving 0-44 for vegetable matter princi- 

 pally.* 



From the several analyses, it will be observed that magnesia is an important and con- 

 stant constituent of the shales and hydraulic limestones. The superior rocks contain a 

 larger proportion than the inferior or g\-pscous deposits. There is no doubt tliis element 

 exerts a beneficial influence on the crops, especially maize and the cereals. The question 

 has been agitated whether magnesian rocks were favorable to vegetation. It seems to be 

 set at rest by observation in New- York, where magnesian rocks are so prevalent. No part 

 of the State is more fertile than those underlaid with the magnesian rocks. The same 

 view is supported by observations in Berkshire (Mass.), v.-here the dolomites prevail. 

 Here the most fertile lands are underlaid by magnesian deposits. When, however, a 

 magnesian limestone is burnt and converted into a caustic condition, the magnesia remains 

 a long time, and if used before it is nearly saturated with carbonic acid and water, it injures 

 vegetation ; but when slacked, it is equally harmless with the air-slacked lime. Without 

 doubt it is an advantage to use the two alkaline earths together, if proper precautions are 

 observed ; for magnesia seems to be as essential to the composition of many grains as lime, 

 and may undoubtedly replace it when the lime is wanting. 



In the western counties, we pass from the Hydraulic or Magnesian limestones to the 

 Onondaga liiuestone : the reason of this has been already explained. This limestone is a 

 hard gray crystalline rock below, but passes upward into a dark shaly cherty rock, which 

 is usually described under the name of Corniferous limestone. It extends from the Hudson 

 river to Blackrock on Lake Erie, forming a belt from three to six miles wide. 



• Jackson's analysis of the Ulster county cement stone, in the Proceedings of the American Geologists and Natu- 

 ralists. 



35* 



