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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 78 



ore deposits are at the contact of granitic rocks with Hmestones. 

 or in veins in diorite. At the Ternares Mine the Hmestone contact 

 zone is characterized by great quantities of velardenite, spurrite, and 

 hillebrandite, minerals first described as new from this locality. 



About a mile from the railroad station in the city of Durango. 

 rises a mass of volcanic rock and iron ore called Cerro Mercado. 



Fig. 59. — Old church on Cerro Remedios, Durango. The rhyolite of 

 this hill is a low grade tin ore. (Photograph by Foshag. ) 



The iron ore deposits of this hill constitute Mexico's chief domestic 

 supply. The iron-bearing mineral is almost entirely hematite, the 

 ferric oxide of iron, and it forms large masses in a rhyolitic rock. 

 Nearly five months were spent in the field and over two tons of 

 specimens collected and shipped. The success of the field-work 

 was largely due to the hearty cooperation of the Mexican govern- 

 ment ofificials and of the American mining engineers in charge of 

 the various properties. 



