250 PSEUDOMORPHOUS MINERALS OF NEW YORK. 



Changes in the Minerals found in the Dolomitic 



LlAIESTONE. 



The minerals which occur in the dolomitic limestones of New 

 York, Westchester and Putnam counties, every where afford the 

 evidence that their chemical composition has been influenced by 

 the nature of their associates. The following are some of the 

 changes which I have observed. 



1. The crystals of white pyroxene wliicli abound in it, fre- 

 quently have a granular texture like the dolomite itself. Some- 

 times parts of the crystals have disappeared, appai'ently by the 

 crumbling of the granular material, which has wholly or in part 

 replaced the pyroxenic matter. Yet the crystalline foi-m is entire- 

 ly preserved. Examples of this kind may be seen at Sing-Sing, 

 Kingsbridge, and at Patterson in Putnam county. 



2. This dolomite often contains a substance with the cleav- 

 age of pyroxene, but which is soft and has a large admixture of 

 carbonates of 1-imc and magnesia. The external characters strong- 

 ly resemble those of some specimens of pyroxene, but the effer- 

 vescence which is exhibited when it is acted on by a dilute acid 

 shows that it is largely mixed with carbonates, 



3. The white ti-emolite, which is also one of the minerals 

 found in this dolomite, exhibits changes similar to those which 

 have been described as applicable to the pyroxene. 



4. As it regards serpentine, the mixtm-es of its different vari- 

 eties with the dolomite and with the pyroxene, would, if reliance 

 was placed merely vipon chemicEil composition, furnish many 

 new and distinct mineral species. 



I do not assert that these changes are produced by heat, which 

 seems at the present day to be marshaUed up on all occasions as 

 the grand geological agent, but it seems to me that they more 

 nearly resemble those which are known to be caused by heat than 

 those M'liich are the result of any other agency. This view too 

 would enlircly accord with the ingenious theory of dolomitisa- 

 tion proposed by Von Buch, and wliich is confirmed by many 

 other facts connected with the occurrence of dolomitic beds in the 



