OF AETS AND SCIENCES. 35 



entire breadth of the Uuited States, the main mass reaching Mexico, 

 but large fragments breaking off and falling during its passage across 

 the country. 



Two irons commonly classed under the general head of" Coaliuila'' 

 have not been included in the above consideration. They are labelled 

 in the Harvard College collection, " Hacienda de Concepcion," * and 

 " San Gregorio Iron, Chihuahua, Mexico," f both bearing the signa- 

 ture of Dr. H. B. Butcher. The specimen of the Hacienda de Con- 

 cepcion was small, and had been hammered, so that its structure could 

 not be conclusively studied, but it appeared to be markedly different 

 from any of the other Mexican irons. 



The San Gregorio iron, of which there were numerous specimens, ap- 

 peared to be made up of very striking octahedral plates, and therefore 

 must be placed among a very different class of irons from the Coahuila 

 group, which it has been the purpose of this paper to describe. 



* Amer. Jour. Sci., 2il series, vol. xix. p. 1G3, 1855. 

 t Ibid., 3d series, vol. ii. p. 336, 1871. 



