8 ANNALS NEW YORE ACADEMY OF SCIEN8ES 



some biotite, hornblende, titanite, apatite, pyrite and zircon. The garnet 

 occurs in small grains closely bunched and cemented by quartz. They 

 appear to be the crushed fragments of originally large garnets. 



An analysis gave 



Per cent 



Si0 2 52.82 



A1 2 3 22.75 



Fe 2 3 1.99 



FeO 9.50 



MgO 2.15 . 



CaO 7.43 



K 2 86 



Na 2 1.23 



H 2 14 



98.87 

 Recasting into the component minerals we obtain 



Per cent 



Quartz 22.44 



Orthoclase 2.78 



Albite 10.48 



Anorthite 8.34 



Grossularite 13.50 



Almandite 14.94 



Hornblende 22.13 



Biotite 1.53 



Corundum 82 



Ferric oxide 2.08 



Glancing over the analysis, we see that this variety of the rock is very 

 low in silica, as compared with the other two phases. It is high in 

 alumina, lime and ferrous oxide. The latter three constituents are in the 

 garnet, thus making it a composite of the grossularite and almandite 

 molecules. There is also a decrease in the amount of soda and potash. 

 On the whole, the rock has the appearance of a contact zone developed 

 from an aluminous and ferruginous limestone, which furnished part of 

 the lime, alumina and iron necessary for the formation of the garnet. 

 Or else the aggregate may be due to the absorption of a mass of impure 

 limestone in the granodiorite. Since Professor Berkey has shown that 

 there are interbedded limestones practically everywhere in the Fordham 

 gneiss, this explanation seems to the writer to be the best. According to 

 Van Hise, 5 combined contact and mechanical action furnish the most 

 favorable conditions for the formation of garnets, which are usually the 



8 Monograph on "Metamorphism," p. 300. 



