326 REVIEWS 



A table shows the correlations of the rocks with the Grand Canyon 

 section. 



Structurally the region forms a part of the Great Basin Province. 

 The faulting, which is especially prominent in the southerly ranges, is 

 of the mosaic type, the displacement being normal for the most part, 

 though thrusts are known, possibly attributable to the crowding inci- 

 dental to block faulting. Excellent plates illustrate the topographic 

 effects of homoclinal structure. Folding is, on the whole, negligible, 

 though some of the field relations might be explained on this basis. The 

 block faulting is supposed to be an expression of larger movements of 

 the same sort, and the great valleys between the four ranges, the Globe 

 Hills, the Pina-Mescal Mountains, the Dripping Springs Range, and the 

 Tortillas, are all thought to have a tectonic rather than a purely erosive 

 origin. 



The ores of Ray and Miami are of the familiar disseminated t3TDe, 

 the ore bodies being large and of tabular form. The metallization did 

 not follow regular or systematic zones of fissuring, but networks of small 

 fractures resulting from widespread disturbance of the rocks. The ore 

 bodies are undulating, flat-lying masses of irregular horizontal outline 

 and variable thickness, and they mostly lack sharp boundaries. The 

 ore body constituting the east part of the Miami-Inspiration zone has a 

 total length of 5,500 feet and a maximum width of 1,600 feet. The 

 average thickness of the Ray ore body is estimated at 120 feet and its 

 maximum at 400 feet. The average thickness of the Miami ore zone 

 has not been estimated, but is somewhat greater. 



The shapes of the ore bodies have been determined largely by exten- 

 sive drilling, and graphs in which the copper assays of drill-hole samples 

 from various depths are plotted, are used effectively to bring out the 

 demarkation between the three principal zones, (i) the leached zone 

 nearest the surface, (2) the zone of sulphide enrichment, and (3) the 

 unenriched protore. 



By far the greater part of the ore in both districts is mineralized 

 Pinal schist; a relatively small amount is mineralized granite porphyry 

 or quartz monzonite porphyry. Drilling at Ray has disclosed important 

 bodies of undeveloped ore in diabase. 



The principal metallic minerals of the protore are pyrite and chal- 

 copyrite. The protore at Miami appears richer than that at Ray, the 

 average of 126 assays under the main Miami ore body being 1.18 per 

 cent. At Ray the copper tenor of the protore usually lies between 

 0.3 and 0.7 per cent. 



