Reviews 



Iron Ores, Fuels and Fluxes of the Birmingham District, Alabama. 

 By Ernest F. Burchard and Charles Butts. With Chap- 

 ters on the "Origin of the Ores," by Edwin C. Eckel. Bull. 

 U.S. Geol. Surv. No. 400. Pp. 204. 



The Birmingham District, as here considered, extends as a long, 

 narrow belt, about seventy-five miles in length by ten in width. The 

 iron ores of the district lie in the broad, anticlinal Birmingham Valley 

 which is structurally a part of the Appalachian Valley. An outline 

 of the geology of the district shows rocks belonging to all the periods 

 from the Cambrian to the Pennsylvanian, with unconformities separating 

 all the systems except the Cambrian and the Ordovician, where the 

 transition is within the Knox Dolomite, which here attains a thickness 

 of 3,300 feet. An unconformity is found within the Ordovician. Within 

 the area are extensive deposits of red hematite and brown ore, and 

 important beds of coking coal and fluxing limestones. 



The red hematite or Clinton ore is found in the Clinton or Rock- 

 wood formation which, in Alabama, consists of lenticular beds of sand- 

 stone and shale with four well-marked ore horizons. The ores occur 

 in lenticular beds analogous to strata, interbedded with limestone, 

 sandstone, and shale. Three opposing theories have been advanced 

 to account for the origin of the Clinton ores: (1) original deposition; 

 (2) residual enrichment by weathering; (3) replacement by percolating 

 waters. Mr. Eckels shows that both the second and third theories are 

 untenable, and that observations support the theory of primary sedi- 

 mentary deposition. 



The brown ores or ores of the hydrous iron oxides belong to a type 

 common in southeastern United States, occurring as irregular masses 

 associated with residual clays, and underlain by limestones of Cambrian 

 and Cambro-Ordovician age. Mr. Eckel points out very forcibly that 

 the decay of a limestone carrying disseminated iron material would 

 not of itself yield such a deposit of ore, but that some factor must be 

 found whereby the iron is concentrated. In his opinion, this concen- 

 tration usually took place in the limestone itself. 



The coke used in the blast furnaces of the district is made from coal 

 mined in the Warrior coal field which lies to the northwest of the valley. 



E. R. L. 

 381 



