142 The Monoclinic Pyroxenes of New York State. 



This was sometimes possible, but at other times the result was 

 not exact, due perhaps to impurities or a slight error in the 

 analysis. In all the analj-ses made by the writer the material 

 was finel}^ powdered and then treated with a magnet and after- 

 wards with a specific gravity solution. 



An examination of the formulae calculated shows the presence 

 not uncommonly, of the wollastonite or orthorhombic pyroxene 

 molecule. There also remains at times an amount of SiOg. 



The analyses further indicate that Tschermak's theory of the 

 relation between AlgOg and the oxides of Ca, Mg and Fe holds 

 good in the case of only about one-half of the New York 

 pyroxenes analyzed, as will be seen from the following table: 



Aluminous Pyeoxenes. 



Ca. Mg4-Fe. Locality. 



.4041 > .3961 Cascadeville. 



.4278 > .3028 Diana. 



.386 > .1847 Keene. 



.31 < .379 " 



.3353 < .4282 Mt. Marcy. 



.3825 < .492 Pitcairn. 



.309 < .373 Pt. Henry. 



.4166 > .2640 Rogers Rock. 



.4107 > .3545 " 



.368 «< .455 .Greenwood Furnace. 



.277 > .189 Rosetown. 



.480 > .375 Warwick. 



.458 > .3655 Edenville. 



.4432 > .4156 Sing Sing. 



.375 > .359 West Point. 



.345 < .453 Willsborough. 



.394 < .419 Edenville. 



Alteration Products. 



Uralitization is the almost universal method of alteration. It 

 begins with the appearance of a fibrous structure on the surface 

 of the crystal, especiallj^ the prism faces, and gradually extends 

 through the entire individual. This change is well shown in the 

 pyroxenes of Russel and Pierrepont. The white varieties alter to 

 tremolite, as shown by the white pja^oxenes of Kingsbridge and 

 Sing Sing, 



These paramorphs of hornblende after pyroxenes are well shown 

 in the gabbros of the Cortlandt Series near Peekskill, where there 



