SIEXITE. -81 



the beds and veins of the magnetic oxide of iron. The great dyke which cuts through 

 Mount McMartin in Newcomb, is sienite. It is also of frequent occurrence in the beds or 

 veins of iron at Adirondack, tliough the rock embracing the ore is hypersthene. It would 

 appear, from these facts, that it is, at least in some instances, to be regarded as of igneous 

 origin. Of its stratification, dip, and value as a mining rock, I might make the same remarks 

 as in the preceding pages, when speaking of gneiss and hornblende. 



Geol. 2d Dist. 11 



