46 



PROCEEDINGS OF WASHINGTON MEETING. 



larger part of the iron-ore belt. They are not confined, to one individual stratum, 

 but occur in various positions in the beds of which they form a small yet charac- 

 teristic part. The upper deposits are extensively developed in Texas, in the area 

 south of those just mentioned, especially in Cherokee, Smith, Rusk, Nacogdoches 

 and other counties. The correlatives of the latter deposits have not yet been iden- 

 tified in Arkansas, and it is somewhat doubtful whether they exist, though certain 

 iron ores in glauconite have been found in the valley of the Ouachita. The eastern 

 extension of the Texas ore-bearing glauconite, however, is probably to be looked 

 for in northern or western-central Louisiana, an area in which the iron ores have 

 not yet been thoroughly investigated. 



Nature of the Ores. 



Though the ores occupying the lower and upper positions just mentioned are 

 much the same in chemical composition, being in both cases hydrous sesquioxides 

 of iron, they differ considerably in their physical character, and may be classified 

 under the two headings of nodular ores and laminated ores. The former represents 

 the lower horizon ; the latter represent the upper or glauconitiferous horizon. 



Nodular Ores. — The nodular ore is characterized by the nodular character of the 

 component parts of the ore beds, though it also occurs in mammillar, stalactitic or 

 botryoidal masses. The nodules are often, and in some places generally', hollow 

 representing geodes, and vary from a fraction of an inch to several feet in diameter. 

 They are frequently cemented together by ore, or by a ferruginous sandstone, form- 

 ing a more or less continuous bed, while at other times they occur loose in the 

 enclosing sands and clays. They generally are partly filled by a yellow, brown, or 





Figure 16 — Ideal Section showing the Mode of Occurrence of the nodular Ores. 

 1 = Sands and sandy clays ; 2 = Ore beds. 



red clay, and sometimes by a ferruginous ochre. They vary from yellow or brown 

 to almost black in color, and the geodes are usually lined on the inside by a brilliant 

 black gloss. Sometimes the outer part of a nodule is an amorphous mass, while 

 the inside exhibits the fibrous character of certain hydrous sesquioxides of iron. 

 The more solid nodules show a concentric structure, the individual layers being 

 often separated by narrow spaces which generally contain more or less earthy 

 matter. Frequently this variety of ore occurs in 1 teds separated 1 >y horizontal layers 

 of sand or sandy clay, the individual beds varying from a fraction of an inch to 

 many feet in thickness. The accompanying ideal section (figure 16) represents a 

 characteristic mode of occurrence of the nodular ores. 



Laminated Ores.— The laminated ore is of a rich chestnut-brown color, often resin- 

 ous in luster. It usually has a more or less laminated structure, which, though it 

 sometimes blends into a massive variety, is generally composed of thin layers 

 varying from a sixteenth to a quarter of an inch in thickness. The laminae are 

 separated by narrow spaces, often containing a gray clay, and are frequently coated 

 with a black gloss. The ore occurs in horizontal beds from one to three feet in 

 thickness, sometimes continuous over many acres, elsewhere in isolated patches. 

 It is composed of masses which are fiat or slightly concave on top, and bulging or 



