CHAPTER III. 



MAGNETITE AND PYRITE. 



2.03.01. Example 12. Magnetite Beds. Beds of magnetite, 

 often of lenticular shape, interstratified with Archaean gneisses and 

 crystalline limestones. They are extensively developed in the 

 Adirondacks, in the New York and New Jersey Highlands, and in 

 western North Carolina. The presence of magnetite in Michigan 

 (Example 9a), in Minnesota (Example 6#), on Shepherd Mountain 

 in Missouri (Example 11), and in Virginia (Example 12) has 

 already been referred to. Other magnetite bodies are known in 

 Colorado, Utah, California, and Wyoming, and will be mentioned 

 subsequently. Titanium is often present in such amounts as to 

 render the ore of no value. The same is true of pyrite and pyrrho- 

 tite. Apatite is always found, although it may be in very small 

 quantity. Chlorite, hornblende, augite, epidote, quartz, feldspar, 

 and a little calcite are the common associated minerals. In New 

 Jersey the beds occur in several parallel ranges or belts. 



2.03.02. Example I2a. Adirondack Region. The magnetite 

 deposits occur in the foothills of the Adirondacks on all sides, 

 and to a less extent in the mountains themselves. The mountains 

 are very largely knobs of a rock, which is chiefly labradorite, with 

 some hypersthene and other bisilicates, and is variously called lab- 

 rador-rock, norite, hypersthene-rock, anorthosite, etc. Whether 

 this is igneous or a series of metamorphosed sediments, it is not yet 

 generally admitted, as the geology of the region largely remains to 

 be worked out. It certainly exhibits both metamorphic and igne- 

 ous facies and is undoubtedly a more or less metamorphosed igne- 

 ous rock. Associated with it, especially in the foothills, are gneiss 

 and crystalline limestones, in the former of which occur the mag- 

 netite deposits now wrought, but field work in the summer of 

 1892 has convinced the writer that there are large bodies of magne- 

 tite in true igneous gabbros in the town of Westport, if not else- 

 where. At Lyon Mountain, on the north, the Chateaugay ore body 



