12 Bulletin of the New York State Museum. 



given in 1797.* The last U. S. census reported the total production 

 to be 85,442 ^ross tons of ore. In 1888 it amounted to 75,000 tons. 



V -THE LIMONITES OF DUTCHESS AND COLUMBIA 



COUNTIES. 



The ore deposits and mines, as here grouped, are in two principal 

 ranges and limestone valleys. First, the Fishkill-Clove belt, stretch- 

 ing north-east, from the Highlands of the Hudson, across the towns of 

 Fishkill, East Fishkill, Beekman and Unionvale ; second, the north- 

 south valley, traversed by the New York and Harlem railway, from 

 the Highlands across Duchess county, and to Hillsdale in Columbia 

 county. The limonite, or brown hematite ore, is found in small 

 pockets of irregular shape, and also in large deposits, which are 

 associated with ochreous clays, and in some cases, with a gray carbonate 

 of iron, in beds underlying it. These ore bodies are wholly in the 

 limestone, or between the limestone and the adjacent slate or schist 

 formations, or they are in the latter, and as a rule of occurrence they 

 are found on or near the dividing line between these formations. 

 Near Fishkill and at Shenandoah the deposits are at the border of 

 the Potsdam sandstone and at the foot of the Archgean ridges. The ex- 

 istence of the carbonate ore in the deeper parts of some of the mines 

 and interstratified with the limestones, is suggestive of the origin of 

 the oxide (limonite) by the decomposition of the ferriferous beds 

 through oxidation and the agency of carbonated waters, and of the 

 great masses of colored clays, also, through the disintegration and decay 

 of the slaty rocks and more argillaceous limestone.f The limestone 

 of these valleys and the overlying slaty rocks have been studied by 

 Prof. Dana, and are referred by him to the Trenton Limestone and the 

 Hudson river slate formations. J 



The ore occurs (1) in large masses, somewhat cellular, having the 

 interstices filled with clays or sandy earths (2) in cavernous and hollow 

 " bombs," often with beautiful mamillary or stalactitic incrustations 

 on the interior, and (3) in irregularly shaped, fragmentary masses, dis- 

 tributed unevenly through the ochreous clays (" ochres") and sandy 



* Bikkinbine ; " The iron ores east of the Mississippi River," in Mineral Resources 

 of the United States for the calendar year 1886, p. 50. 



t For a clear arid concise statement of the origin of these ores see "Note on the 

 making of Limonite ore beds," by Peof. Jambs D. Dana, in Am. Jour, of Science (3), 

 vol. XXVI II: pp. 398-400. 



X Am. Jour. Science (3), vol. XVII : pp. 375-388 and vol. XXIX : pp 205 et seq. 



