168 Agricultural Geology of Onondaga County. [April, 



One hundred grains of the powdered rock, when acted upon a 

 few days by cold water, dissolves one grain, of which there re- 

 mains after ignition .56 of a grain, leaving .44 of vegetable 

 matter. 



From the several analyses it will be observed that magnesia is 

 a constant element in the rocks, from the red rock to the superior 

 portion of the rocks belonging to the hydraulic lime series. In 

 Onondaga county the series terminates in a mass about four feet 

 thick, whose structure is remarkably concretionary, and exceed- 

 ingly irregularly bedded. It is all that remains of the penta- 

 merus limestone, which in Albany and Schoharie counties is from 

 fifty to sixty feet thick. In Ulster county it is the rock employed 

 for cement. Several other rocks have also thinned out towards 

 the west, in consequence of which the Onondaga limestone re- 

 poses upon the thick bedded masses of the hydraulic limestones; 

 excepting that sometimes the Oriskany sandstone occasionally 

 intervenes between the latter and the former. In some places it 

 is indicated by the presence of a thin layer of sand only, or a 

 few small boulders; in others it is eighteen inches thick. 



We pass at once to the Onondaga limestone, by which name 

 we include all the upper part which is usually separated from the 

 lower, and has been called the cor^iiferous limestone, or limestone 

 which bears hornstone. This rock is regarded as a pure lime- 

 stone, leaving out of view, the layers and irregular masses of horn- 



•Dr. Jackson's analysis of Ulster county cement stone, in the Proceedings 

 of American Geologists and Naturalists. 



