450 ABSTEACTS: GEOLOGY 



GEOLOGY. — Possibilities for manganese ore on certain undeveloped 



tracts in Shenandoah Valley, Virginia. D. F. Hewett, G. W. 



Stose, F. J. Katz, and H. D. Miser. U. S. Geological Survey 



Bulletin 660-J. Pp. 26, with maps, and sections. 1918. 



Most of the manganese deposits occur in banded clays that are 



believed to have been derived by weathering in place from the lower 



200 feet of the Shady dolomite which rests on the Erwin quartzite. 



In most places the local structure of the adjacent rocks has determined 



the form of the deposits and in large measure their areal extent and 



their persistence below the surface. The tracts that are considered 



favorable for the occurrence of manganese or manganiferous iron ore 



are underlain by troughs of the upper beds of the Erwin quartzite, 



from the surface of which the products of decay of the overlying Shady 



dolomite have not been removed. 



The manganese seems to have been originally widely disseminated 

 as carbonate in the limestone and dolomite in the neighborhood of the 

 deposits. It was dissolved as bicarbonate and transported along estab- 

 hshed channels of circulation to the places where the oxides are now 

 found. The oxides were probably deposited when and where the 

 solutions containing manganese bicarbonate met oxygen-bearing 

 waters. According to the hypothesis structural troughs were the most 

 favorable channels for circulation, and if suitable conditions for oxida- 

 tion and deposition existed they should be the most favorable places 

 for accumulation. 



Six undeveloped tracts along the west front of the Blue Ridge are 

 described in which prospecting with a view to the discovery of man- 

 ganese deposits is recommended. 



R. W. Stone. 



G'EOLOGY .—Manganese at Butte, Montana. J. T. Pardee. U. S. 

 Geol. Survey Bull. 690-E. Pp. 20. 1918. 



Rhodochrosite, rhodonite, and manganese oxides are abundant at 

 Butte. Rather curiously, manganese minerals are scarce in the veins 

 that yield copper ore, but in a peripheral zone commonly known as the 

 silver area, manganese minerals are plentiful. The width of the zone 

 in which the veins are strongly manganiferous ranges from 1 to 2 miles 

 approximately, being greatest toward the west. 



About half of the manganiferous zone lies north of the copper area 

 and east of the rhyolite. Though manganese is widely distributed in 

 all parts of the zone, it appears to be relatively most abundant in the 

 southwestern section. It occurs abundantly as deep as the workings 



