192 REVIEWS 



are the economic values. Other pecuHar mineral constituents are blue, 

 opalescent quartz, hypersthene, and hornblende derived from pyroxene. 

 Named in order of their probable differentiation, the principal rock types 

 of the area are: biotite-quartz, monzonite-gneiss, syenite formerly 

 referred to as pegmatite, gabbro, nelsonite, and diabase. 



The geology of the ore deposits is fully discussed with especial 

 description of the unusual rock types. The ore minerals occur most 

 abundantly in the nelsonite. The chief constituents of this rock are 

 apatite and ilmenite; there are varieties of nelsonite which are rich in 

 rutile. The nelsonite bodies are of remarkably uniform granularity, 

 irrespective of the size or of the width of the body. Some show evidence 

 of mineralogical gradation into the composition of the wall rock, whereas 

 others show sharp differentiation of the nelsonite and the inclosing rock. 

 It is supposed that the nelsonite dikes were intruded into the still very 

 hot, and possibly in some places unsolidified, rock. The rutile-rich 

 bodies appear to have been formed in advance of the ilmenite nelsonites ; 

 this is suggested by their irregularity in boundary, and by their appear- 

 ance of transition into the surrounding rock like segregations rather 

 than intrusions. Both types are regarded as differentiation facies of the 

 inclosing rocks. 



This district contains the richest and greatest known deposit of 

 titanium minerals in the world. With an increase in the utilization of 

 titanium' products it is expected that this will become a productive min- 

 ing region. The apatite deposits will not be of much importance com- 

 mercially while Florida remains as productive of phosphates as at present. 

 The Virginia deposits both of titanium and of apatite have been worked 

 intermittently but the present output is insignificant. 



T. T. Q. 



The Ore Deposits of Northeastern Washington. By Rowland 



Bancroft. U.S. Gaol. Surv. Bull. No. 550. Pp. 215, figs. 26; 



pis. 19. 



Except for a brief discussion of the general geologic features of northeastern 



Washington by way of introduction, this bulletin is given over for the most 



part to descriptions of mines and prospects in the various districts included. 



In the discussion of each district some attention is given to the origin of the 



ores, but the discussion is broadly general. A section on the Republic District, 



written by Lindgren, is included in the volume. 



A. D. B. 



