1151 ((imposition OF LIMESTONES, 



XIII. A SERIES OF TABLES, SHOWING THE COMPOSITION OF THE LIME- 

 - ["ONES, SHALES, SLATES AND MARLS OF NEW-YORK; 



TOGETHER WITH REMARKS WHICH ARE DESIGNED TO SHOW THEIR PROBABLE INFLUENCE UPON TH1 

 [POSITION OF THE SOILS IN CONNEXION WITH T1IE.M. 



Limestones of new-york. 



The geological formations embraced in the limits of the State, contain deposits of this 

 rock. The superior part of the Silurian system, and the Old Red or Devonian of recent 

 authors, are quite deficient in limestones, as has been already stated in the foregoing pages. 

 The Primary system, however, is rich in limestone; hut its qualities are usually defective, 

 in consequence of its containing insoluble matter, as silica or quartz, mica, pyroxene, 

 hornblende, etc In the specimen of which 1 have given an analysis, which was taken 

 from the beds in gneiss at the Natural bridge, Jefferson county, scarcely a trace of magnesia 

 was found. This was an unexpected result, inasmuch as it is often associated with ser- 

 pentine and other magnesian minerals. It may have happened that wherever magnesia 

 and the other necessary elements were contained in the rock, the] hare been converted 

 into serpentine, and the serpentine itself has been separated from the mass of limestone 

 by segregation. The beds of primary limestone require no farther notice, as they r have 

 been fully described already. 



The Taconic limestones are frequently magnesian, or doloniitic, as they have been 

 called : and from my own examinations, I believe that all the beds which contain tremolile 

 are magnesian. It appears, however, from the lamented Olmsted's analyses for the Ver- 

 mont survey, that many of the friable limestones of this system are nearly pure carbonates 

 of lime, and are destitute of magnesia. 



The Sparry limestone was also found to be destitute of magnesia, at least so far as the 

 specimen examined was concerned. 



The limestones at the base of the Silurian system are quite magnesian, especially the 

 Calciferous sandstone, and parts at least of the Trenton limestone. The Birdseye, and the 

 Isle Lamotte marble, appear to be destitute again of magnesia, the latter containing only 

 3 or 4 per cent. 



The Niagara limestone of the Ontario division can scarcely' be called magnesian. The 

 shales below contain some magnesia and soda ; the latter, as it appears from the decom- 

 posing materials which are located in favorable spots, exists in large proportion. 



The limestones become magnesian again in the lower pan of the Helderberg division, 

 especially the water limes. Magnesia is contained in the slaty thin-bedded, as well as in 

 the thick-bedded limestones. 



The Onondaga limestone is a pure limestone, or, in other words, is not magnesian. 



The limestone of the Marcellus slate, as it occurs at Schoharie, Cherryvalley and Man- 

 lius. is probably magnesian : it has not been examined for this substance. 



