ECONOMIC GEOLOGY 221 



also in large deposits, which aire associated with ochreous clays, 

 and in some cases, with a gray carbonate of iron, in beds under- 

 lying 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 Cam- 

 brian sandstone and at the foot of the Archaean ridges. The 

 existence 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 fer- 

 riferous 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 argil- 

 laceous limestone. The limestone of these valleys and the over- 

 lying slaty rocks have been studied by Prof. Dana, and are re- 

 ferred by him to the Trenton limestone and the Hudson river 

 slate formations. 



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 mammillary or stalac- 

 titic incrustations on the interior, and, (3) in irregularly shaped, 

 fragmentary masses, distributed unevenly through the ochreous 

 clays (' ochres ') and sandy earths. 



The earliest iron manufacture in the state was in Columbia 

 county, on Ancram creek, and was probably on these ores. 



THE LIMONITES OF STATEN ISLAND 



The group of iron mines on Staten Island is in a superficial 

 deposit probably derived from the underlying rock in the process 

 of decomposition which has produced the serpentine of that 

 region. , 



THE CARBONATE ORES OF THE HUDSON RIVER 



The mines of spathic iron ore, or carbonate ore, are in the 

 valley of the Hudson river, in Columbia county, south of the city 

 of Hudson, and in Ulster county near Napanoch. The mines 



