384 REVIEWS 



Notes on the Unaweep Copper District, Colorado. By B. S. Butler, 

 U.S. Geol. Surv. Bull. No. 580-B, pp. 19-23. 



Notes of a two-day reconnaissance. The ores occur in fissures cutting 

 both igneous and sedimentary rocks. The district is practically idle, and has 

 never advanced beyond the prospecting stage. 



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Some Cerusite Deposits in Custer County, Colorado. By J. Fred 

 Hunter. U.S. Geol. Surv. Bull. No. 580-C, pp. 24-37. 

 Figs. 5- 

 Describes the deposits of cerusite 12 miles northeast of Silver Cliff. The 

 ores are in a crushed fault zone. The mines have been idle for more than 

 ten years. The two days spent in the field by the author preclude the possi- 

 bility of any exact statements regarding either the general geology or the ore 

 deposits. .... 



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The Grand Gulch Mining Region, Mohave County, Arizona. By 

 James M. Hill. U.S. Geol. Surv. Bull. No. 580-D, pp. 38-58. 

 Figs. 10. 



"The ore bodies occur around the sides of a plug-like mass of rock, which 

 is sedimentary in origin but is entirely unlike the rocks that enclose it." The 

 ore bodies, carrying copper, are more or less lens-shaped replacements of the 

 rocks in which they are found. The author shows interesting drawings of 

 the relation existing between chalcopyrite, bornite chaleocite, and malachite, 

 as successive steps in the alteration of the primary sulphide. 



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