THE IRON SERIES (IN PART). 79 



from the iron of the glauconite itself. The second group occur 

 just north of the last, and have probably resulted from the altera- 

 tion of clay ironstone nodules (Cf . Example 5), while the third has 

 formed in the streams by the erosion of the first two and from the 

 smaller ore-streaks and segregations. Limonite also occurs in 

 northwestern Louisiana. (Mineral Resources, 1887, p. 51.) Limon- 

 ite is known in a number of localities of Colorado. The chief pro- 

 ductive mines lie in Saguache County, near Hot Springs. They 

 furnish a most excellent ore from cavities in limestones, which are 

 generally, but with no great certainty, considered Lower Silurian. 

 R. Chauvenet states that the ores yield about 43$ Fe in the 

 furnace. 1 



A great body of limonite nodules, bedded in red, residual clay r 

 has been reported from the Clinton series of Allamakee County, 

 Iowa. (E. Orr, Amer. Geologist, Vol. L, p. 129.) 



Much limonite occurs at Leadville in connection with the lead- 

 silver ores, and is used as a flux by the lead smelters. Some grades 

 low in silver and rich in manganese have even been used for spiegel 

 at Pueblo. For the geological relations, see Example 30. 



2.01.16. Limonites in supposed Carboniferous limestone occur 

 in the East Tintec mining district in Utah, and seem to be as- 

 sociated with a decomposed eruptive rock, somewhat as at Lead- 

 ville. The limonite is chiefly used as a flux by lead-silver smelters. 2 



2.01.17. Example 2a. Siluro- Cambrian Limonites. Beds of 

 limonite in so-called hydromica (talcose, damourite), slates and 

 schists, often also with limestones of the Cambrian and Lower 

 Silurian systems of the Appalachians. The great extent, the geo- 

 logical relations, and the importance of these deposits warrant their 

 grouping in a subtype by themselves. They extend along the Ap- 

 palachians from Vermont to Alabama, and are in the " Great 

 Valley," as it was early termed, which marks the trough between 

 the Archaean on the east and the first corrugations of the Paleozoic 

 rocks, often metamorphosed, on the west. The masses of limonite 

 are buried in ocherous clay, and the whole often preserves the gen- 

 eral structure of the schistose rocks which they have replaced. The 



1 R. Chauvenet, ' ' Preliminary Notes on the Iron Resources of Col- 

 orado," Ann. Rep. Colo. State School of Mines, 1885, p. 21 ; "Iron Re- 

 sources of Colorado," M. E., 1889. F. M/Endlich, Hayderis Reports, 1873,. 

 p. 333. B. T. Putnam, Tenth Census, Vol. XV., p. 482. C. M. Rolker, 

 " Notes on Certain Iron Ore Deposits in Colorado," M. E., XIV. 266, Rec. 



2 B. T. Putnam, Tenth Census, Vol. XV., p. 490. 



