B. Silliman — Iron Ore of Mexico. 377 



ties, by Mr. Derby in his paper published in May of this year.* 

 All are firmly attached to the massive ore, some masses of which 

 in my hands weigh ten to twenty pounds. There is nothing in 

 the mode of occurrence of this ore, or in the chemical const! tu- 

 sh lends any support to the opinion of Grorceix that 

 raartite is derived from the transformation of pyrite. In sup- 

 port of this statement I am permitted to cite the analysis of an 

 average sample made up from twenty-seven pieces of the 

 Durango ore collected by Mr. Birkinbine, and submitted by 

 him to Mr. Andrew S. McCreath, chemist to the second Geo- 

 logical Survey of Pennsylvania, being a commercial sample of 

 the whole ore mass and not presenting fairly the constitution of 

 the pure mineral. This "sample "gave the following Jesuits. 



>n 55 "8 per cent. A purer specimen 

 I gave separately 62775 per cent metallic iron. 

 The powder of this ore is attracted by the magnet, but frag- 

 ments of the size of grains of wheat are not affected by a mag- 

 net of moderate power. 

 This enormous mass of valuable iron ore, thanks to the near 

 i »f the railwav system of Mexico, is now likely to 





2. Sinaloa iron ores. 



In this connection it is interesting to note the chemical eom- 

 l"'>Uion of certain other ores of iron from the State « 



M'-xieo, also placed at my disposition by Mr. North. The 



rere made in the Iron Masters' Laboratory, Philadel- 



. Blodgct Britton. In these the transformation of 



. has proceeded only so far as to leave still 



" 



1 ■-" vm,;.;,-.., ..i-,. ,,„„,. .,.,.. ,'.) v ;,[,,.,.;. ..1 i,, the ma-net. Tln-v 



are from Tepuche, Bescuino and Cosolu. 



* This Journal, III, xxiii, p. 373. 



