PSEUDOMOKPHOUS MINERALS OF NEW YORK. 253 



same agent or not, I still think it probable that they have been 

 afterwards subjected to heat. This seems to have been necessa- 

 ry to give them the peculiar appearance which they now exhibit. 

 Such are the facts which I have observed in regard to the para- 

 sitic formation of minerals in the state of New York. The fol- 

 lowing are some of the inferences w^hich seem to me to be fairly 

 deducible from them. 



1. Many crystalline minerals have undergone changes in their 

 chemical composition subsequently to the period of their crystal- 

 lization. The changes which have taken place in crystals of 

 quartz, and magnetic iron ore, may be referred to as examples. 



2. The foreign bodies which must have been associated with 

 some minerals at the moment of crystallization, have not in the 

 least degi-ee interfered with the regularity and beauty of the crys- 

 talline form. This inference is supported by the facts in regard 

 to the masses of anthracite found in the most perfect quartz crys- 

 tals of Herkimer county, &:c. 



3. The probable intrusion of foreign matter into the substance 

 of crystals, after a portion of the original constituents of these 

 crystals has been removed, without any change of crystalline 

 form, and that too without reference to the isomorphous rela- 

 tions of the removed and the replacing bodies. Under this head 

 I may refer to the notices which I have introduced of the changes 

 in the hornblendic and pyroxenic minerals, &c. 



4. In regard to the general agency by which these changes 

 have been produced, it seems to me to be fairly deducible from a 

 review of all the facts which have been presented, that although 

 aqueous solution may in some instances have been the means of 

 removing some of the constituents of the altered mineral, the in- 

 trusion has been the result of igneous action. The bent crystals 

 of the grayish hornblende, the fused appearance of the crystals 

 of quartz and apatite in the county of St. Lawrence, near the 

 deposites of steatitic pyroxene, and the occurrence of various vol- 

 canic products in the vicinity of the altered minerals of the dolo- 

 mite of Putnam, Westchester and New York, may be adduced 

 as proofs of the correctness of this inference. 



