44 The American Naturalist. [January, 



Compact hornblende is noted as an alteration product of its augite. 

 Where in contact with the limestones the gabbro has changed these 

 rocks into masses of green pyroxene, garnet, scapolite and sphene. A 

 second variety of the gabbro is hypersthenic. A third variety is char- 

 acterized by its large zonal feldspars composed of cores of plagioclase 

 surrounded by microperthite, although crystals of the latter substance 

 alone abound in some sections. The ferromagnesian components are 

 rare as compared with the feldspars. Nearly all specimens of these 

 rocks are schistose, and all of the schistose varieties exhibit the cata- 

 clastic structure in perfection. Analysis of the normal (I) and of the 

 microperthitic or acid (II) gabbros yielded : 



Si0 2 A1 2 3 FeO MgO CaO K 2 Na 2 H 2 Total 

 I 57.00 16.01 10.30 1.62 6.20 3.53 4.35 .15 = 99.16 

 II 65.65 16.84 4.01 .13 2.47 5.04 5.27 .30 = 99.71 



Near the contact with the limestone the gabbro is finer grained than 

 elsewhere. Pyroxene is in larger grains than in the normal rock, but 

 the feldspar is in smaller ones. The limestone loses its banding and is 

 bleached to a pure white color. Between the two rocks is a fibrous 

 zone of green pyroxene and wollastonite.together with small quantities of 

 sphene and garnet and sometimes scapolite and feldspar. The red 

 gneisses, common to that portion of the region studied which borders 

 on the gabbro, are thought by the author to be largely modified por- 

 tions of the intrusive rock. 



The Eastern Adirondacks have been studied by Kemp.* The lime- 

 stones of Port Henry consist of pure calcite, scattered through which 

 are small scales of graphite, phlogopite and occasionally-quartz grains, 

 apatite and coccolite. This is cut by stringers of silicates that are 

 granitic aggregates of pi rnblende and a host of 



other minerals. Ophicalcite masses are also disseminated through the 

 limestones, and these are also penetrated by the silicate stringers. 

 Merrill 3 has shown that the serpentine of the ophicalcite is derived 

 from a colorless pyroxene. The schists associated with the limestones 

 are briefly characterized by the author. At Keene Center a grauulite 

 was found on the contact of the ophicalcite with anorthosite. 



Hornblende Granite and Limestones of Orange Co., N. Y. 

 —Portions of Mts. Adam and Eve at Warwick, Orange Co., N. Y., are 

 composed of basic hornblende granite that is in contact with the white 



