R. T. Hill — Hematite and Martite of Mexico. 119 



descriptions, however, the massive Cretaceous limestones of 

 Mexico were generally supposed to be of Paleozoic age, and 

 the difficulties of liability to mistake the superficial martite of 

 the hematite deposits for magnetite has already been cited in 

 the experiences of Mr. Birkinbine, Prof. Silliman and the 

 writer. Mr. Manross himself remarks that " what is still 

 lacking is the evidence of the fossils " to prove that a coal 

 vegetation has once existed in these latitudes." Senor Cas- 

 tillo, upon his geological map of Mexico gives no sedlmen- 

 taries of Paleozoic age in this region, the only ones indicated 

 being Cretaceous. He does give metamorphic and primitive 

 rocks however and eruptives, and the Archaean which has been 

 reported east of this State may extend into it. 



In conclusion it may be said that the occurrence of such 

 large masses of hematite in rocks of Cretaceous and Tertiary 

 age is of great interest, and that the Mexican ores of this 

 character, accompanied by martite have a wide occurrence in 

 that republic, which will be an important factor in the future 

 iron supply of the world. Prof. Frazer remarks that it would 

 pay to import these ores for mixture, as Cuban ores are now 

 imported. Ten years ago Prof. Silliman said of the Durango 

 iron : " The enormous mass of valuable iron ore, thanks to the 

 near approach of the railway of Mexico, is now likely to become 

 of commercial importance." Exactly ten years from the 

 month of publication of his article the Mexican International 

 railway celebrated the completion of its line to the foot of the 

 Durango iron mountain, connecting it by rail with the coal 

 fields of the Sabinas, and the prophecies of Profs. Silliman and 

 Birkinbine are on the eve of fulfillment. 



The accompanying note by Mr. Whitman Cross upon the 

 eruptive rocks of Coahuila are of interest in connection with 

 the discussion of the iron deposits. The general geology of 

 the region will be given in another paper. 



Igneous rocks from the Coal and Iron regions of Coahuila 

 and Nxieva Leon, Mexico, collected by R. T. Hill / by 

 Whitman Ckoss. 



1. Basalt overlying Laramie coal fields. — Mesa, 6 miles east 

 of Santa Rosa de Musquez. A rock of simple normal constitu- 

 tion. Olivine crystals in various stages of decomposition are 

 the only porphyritical constituent. Groundmass of small 

 plagioclase staves and augite grains. There seems to be no 



Am. Jour. Sci.— Third Series, Vol. XLV, No. 266.— February, 1893. 

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