ADDENDA. 281 



ore. Such as have been found are practically all limonite or brown 

 hematite, and are generally very low in iron. The ores occur in 

 five districts, viz.: Northeastern Arkansas, northwestern Arkansas, 

 the valley of the Arkansas River, the Ouachita Mountains, and 

 southern Arkansas. They are generally associated with sand- 

 stones or cherty limestones. The first-named district makes the 

 best showing. In it the ores are in Lower Silurian (Calciferous or 

 lower) sandstones, cherts, and limestones. In the second district 

 they are in Lower Silurian cherts and Lower Carboniferous sand- 

 stones. In the third, they occur with Carboniferous and Lower 

 Carboniferous strata, but are also in the form of recent spring de- 

 posits. In the Ouachita Mountains they are with Lower Silurian 

 shales and novaculites. In this district the magnetite of Magnet 

 Cove occurs, but it is only an interesting mineral and not in any 

 practical quantity. The last district has the ores in sands and 

 clays of the Eocene. Its continuation in -Texas and Louisiana has- 

 been already mentioned in the main text. 



Page 122. Too little attention was given to titaniferous mag- 

 netite in the text ; for although these ores are not now of value, 

 they are exciting considerable attention and are of great scientific 

 interest. They are almost invariably in wall rock that consists of 

 plagiocla&e, with augite, hypersthene, and hornblende, one or all. 

 The rock may thus be gabbro, norite, or diorite, and is of igneous- 

 (plutonic) character. The ores appear to be excessively basic de- 

 velopments of the wall rock, which were formed during its cooling 

 and crystallization. Subsequent metamorphism, mountain-making 

 processes and the like, sometimes give them a gneissic structure, 

 and stretch out the ore into apparent beds. In the great series 

 of these labradorite rocks which is so extensive in Canada, and 

 which was called by T. Sterry Hunt the Norian, these ores 

 are very abundant. The same rocks form the central Adiron- 

 dacks and contain some enormous bodies of titaniferous ore. 

 Prof. E. Emmons of the New York Geological Survey in 1835-40 

 gives much space to them as occurring near Lake Sanford and 

 Lake Henderson. 1 The later Survey of Uno Sebenius has indi- 

 cated an even greater extent than was known to Emmons, although 



1 E. Emmons, Rep. on Second District, N. Y. State Survey, pp. 244- 

 255, 1842. A. J. Kossi, " Titaniferous Ores in the Blast Furnace," Trans. 

 Amer. Inst. Min. Eng., February, 1893. J..C. Smock, Bulletin of A'. F. 

 State Museum, p. 37. 



