SIENITE. 
81 
the beds and veins of the magnetic oxide of iron. The great dyke which cuts througli 
Mount McMartin in Newcomb, is sienite. It is also of frequent occurrence in the beds or 
veins of iron at Adirondack, though 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 
