26 SMITHSONIAN INSTITUTION 



bodies of Santa Eulalia, aside from their great economic importance 

 are of unusual geological interest. They are in the form of huge 

 chimneys that cut across beds of limestone. From these chimneys 

 lateral extensions called iiiaiifos extend for variable distances hori- 

 zontally. One such niaiifo which we examined in the Mina Yieja 

 Mine had been followed for two miles from its source and had been 

 in continuous ore. 



Our last work was done at Los Lamentos revisiting the Ahumada 

 Mine. The ore body of this mine consists of a continuous manto 

 that follows the contact between a hne-grained blue limestone and a 

 highly fossiliferous pink to light gray one, and is characterized by an 

 aureole of dolomitized limestone about it. Beautiful specimens of 

 various lead minerals, wulfenite, vanadinite and descloizite are often 

 abundant at the Ahumada Mine and make very desirable display 

 specimens. Some choice material w-as collected and the study of the 

 deposit considerably extended. 



The field-work in Sonora was undertaken with money from the 

 Roebling Fund. Later work was in collaboration with the Miner- 

 alogical IMuseum of Harvard I'niversity. For the successful field- 

 work I am indebted to a nunil)er of the mining men of Mexico, with- 

 out whose active cooperation little could have been accomplished. 



