The MonocUnic Pyroxenes of New York State. 131 



(AlFe)2Si06. The color is usually green to black, and the habit 

 of the crj'stals is short and stout. 



Leueaugite is a name given to white or gra,yish varieties, with 

 alumina, lime, magnesia and little or no iron. 



The varieties described above are purely theoretical and na 

 fixed line of division exists, for all stages of transition in com- 

 position between the different ones ma}^ occur. 



In treating of the pja'oxenes of New York State the writer 

 has for convenience set an arbitrary line of division, classing as 

 diopside those with less than S%> of alumina and as augite those 

 containing more than that amount. 



Distribution of the Pyroxenes in New York State. 



There is in the eastern portion of New York State an exten- 

 sive area of igneous and metamorphosed rocks which are bor- 

 dered by the Cambrian and Silurian strata of sedimentary origin, 

 and into which they have often penetrated. Where the limestone 

 is in contact with the igneous rock it not only becomes more 

 coarsely crystalline, but there are also developed in these contact 

 zones a number of minerals chief among which are pyroxene, 

 amphibole, wollastonite, scapolite, garnet, tourmaline, feldspar, 

 titanite, zircon. 



This large igneous area forms the Adirondack massif west of 

 Lake Champlain, and which extending through Clinton, St. Law- 

 rence, Essex and Jefferson Counties, includes a series of (Ref. 

 29 and 30) quartz-orthoclase gneisses with biotite or augite, crys- 

 talline limestones often shading to ophicalcites on the east and 

 closely associated with black hornblendic and pyroxenic gneisses 

 on the west, and thirdly a great series of intruded plutonic rocks 

 on the Gabbro family. 



In this region the pyroxene occurs in the form of small grains 

 and crystals as a primary constituent of the gabbros and gneisses,, 

 as well as in the limestones and ophicalcites at or near their con- 

 tact with the intrusive masses. In the limestone, the pyroxene 

 begins to appear in scattered grains as the contact is approached, 

 and these increase in number and degree of development until at 

 the contact the limestone is often filled with an interlacing mass 

 of crystals while between it and the intrusive there is often a 

 space lined with well-formed and sometimes quite large pyroxene 

 crystals. Other minerals may occur as well, and the space be- 



