H. T. Rill — Hematite and MaHite of Mexico. 117 



form the slopes of the mountain as a talus." . ..." I am free 

 to say that after having visited the iron mines of the United 

 States, I have found nothing as yet to compare as to quantity 

 in sight with the Cerro de Mercado of Durango." Unfortu- 

 nately there has been no attempt at a description of the 

 geology of this mass except that given by Wiedner,* whose 

 allegation that it is the cone of an ancient volcano is erroneous, 

 as can be seen by referring to Mr. Birkinbine's excellent pic- 

 ture of the mountain which was reproduced in this Journal. f 

 The only mention throwing light upon the nature of the 

 country rock is that given by Prof. Silliman, who says :;{; 

 " From samples of the country rock which I find in Mr. 

 North's collection the (enclosing) walls are of purple por- 

 phyry; which would indicate that the Durango mass is 

 accompanied by eruptive rocks as in the other cases men- 

 tioned." Inasmuch as the iron has been smelted for many 

 years in primitive furnaces, requiring fluxes without rail 

 transportation, it is very probable that the Comanche lime- 

 stone (the chief sedimentary rock of Durango) cannot be 

 very far distant from the mines. Prof. Silliman's descrip- 

 tion of the martite and hematite ores of Durango makes them 

 appear to coincide so perfectly with those of Monclova, that it 

 is difficult to believe otherwise than that the two deposits are 

 geologically related. 



Jalisco. — Iron has been smelted for many years in this 

 State, in the vicinity of Tula, southwest of Guadalajara. The 

 deposits have been briefly described by Mr. J. P. Carson. § 

 According to this writer, the ore occurs in four distinct dis- 

 tricts. The Amole mine in the district of Tula is bounded on 

 one side by ' ; a trap dyke" and on the other by a shaly dis- 

 jointed sand rock. In the other districts the ore occurs under 

 conditions similar to those of Monclova. In the district of 

 Chiquilistlan, Mr. Carson says " the formation is limestone — 

 probably Tertiary — greatly upheaved by volcanic action and 

 penetrated in various directions by volcanic dykes." In the 

 Tecotes mine the " vein is what is termed segregated, occu- 

 pying a space between parallel seams of limestone." The Los 

 Animas mine, which he says can be traced for a distance of 

 over one thousand feet is also in a segregated vein of lime- 

 stone." These limestones, instead of being Tertiary, as con- 

 ditionally stated by Mr. Carson, are very probably the Coman- 

 che limestones of the Cretaceous, for Barcena describes them 

 as Cretaceous and gives a list of fossils which are char- 



* Quoted by Mr. Birkinbine. 



f See Prof. Silliman's paper previously cited. % Loc. cit. 



§ Iron Manufacture in Mexico, by J. P. Carson ; Trans. Am. Inst. Mining- 

 Engineers, vol. vi, 1887-88, pp. 399-415. 



