216 NEW YORK STATE MUSEUM 



mines map. The geology of a county or district gives the clue 

 in searching for ore; and its importance can not he too strongly 

 stated, both as a guide, suggesting exploration, and warning 

 against unnecessary and fruitless surveys and wasteful outlays 

 of time and money. For example, the magnetites 'belong to the 

 crystalline rock districts, and the search for them in the later, 

 sedimentary rocks of the adjacent territory would be a hopeless 

 task; or, again, the exploration of the Highlands or Adirondacks, 

 for carbonate ores, would be equally unscientific and destitute 

 of good results. 



The geological formations, which are characterized as definite 

 ore horizons, become the basis of a natural arrangement of the 

 ore districts of the state. They are well marked geographically 

 also. 



Following this geologico-geographical arrangement, the groups 

 and iron-ore districts are: 



1 The Highlands of the Hudson.— Magnetic iron ores. 



2 The Adirondack region, including the lake Champlain mines.— 

 Magnetic iron ores, 



3 The hematites of Jefferson and St Lawrence counties. 



4 The Clinton or fossil ores. 



5 The limonites of Dutchess and Columbia counties. 



6 The limonites of Staten Island. 



7 The carbonate ores of the Hudson river. 



A few isolated mines can not be thus classified, as the hematite 

 near Canterbury, Orange county, Ackerman's mine near Union- 

 ville, Westchester county, the Napanoch and Wawarsing mines, 

 in Ulster county, the hematite of Mt Defiance in Ticonderoga,' 

 and the bog iron ores which are scattered in all of the great 

 divisions of the state. The iron sands of the shores of Long 

 Island are left out, as not properly a natural source of iron. 



MAGNETIC IRON ORES 

 The Highlands of the Hudson 



Magnetite is one of the common minerals in the crystalline 

 rock region of the Highlands. It occurs as an accessory con- 

 stituent in the granitic and gneissic strata; and by itself, forms 



