ECONOMIC GEOLOGY 



217 



beds of considerable extent and thickness. Accordingly as it is 

 more or less free from foreign minerals it is rich or lean, varying 

 from the pure magnetic iron ore which contains 72.4% of iron 

 to rock containing only traces of iron in its mineralogi- 

 cal composition. The beds of ore show lamination and 

 are faulted, folded and contorted as the inclosing strata 

 of rock, and have the same general strike and dip in common 

 with the latter. They are generally of irregular form, in places 

 widening into thick deposits or lenticular shaped masses, in 

 others contracted in thin sheets, which are not mined profitably. ' 

 The ore is found in some cases to separate into thin layers, and 

 masses of rock (' horses ') are met with entirely surrounded by 

 the ore. The phases of variation are almost as many as there 

 are mines, where they can be studied. In the larger and older 

 mines the ore has been followed for thousands of feet in the line 

 of strike or on the course of the ore, and for hundreds of feet in 

 depth (on the line of dip) without reaching its limits. Owing to 

 the unprofitable nature of working such thin ore beds, they are 

 often not followed to the end, and the real extent of few of these 

 ore deposits is known. In general, it may be stated that in this 

 region the ore beds stand nearly on edge and have a northeast 

 and southwest ^strike and a descent or dip at a isteep angle to the 

 southeast. In consequence of their highly inclined position and 

 their irregular shape these ore bodies are called ' veins,' less fre- 

 quently ' chimneys ' and ' shooitls ' of ore. 



The magnetic iron ore has not been found distributed uni- 

 formly throughout the Highlands. There appear to be certain 

 ore ranges or belts in which the larger and more productive mines 

 are opened. There are mine groups also, a-s the Sterling Iron and 

 Railway Company's mines, the Greenwood mines, in Orange 

 county; the Todd-Oroft and Sunk mines, and the Oroton- 

 Brewster ranges in Putnam county. The boundaries of these 

 overbearing -belts and the intermediate barren territory have not 

 been determined, since the exploration has been largely made by 

 individual effort and without any general plan covering the 



whole area. 



Mines have been opened in Orange, Rockland, Westchester 



