1034 General Nates. [December, 



analyses, such as would have contented most writers, while 

 chemical analyses are often needed to establish the identity of a 

 species. The broader study of the origin of species can be done 

 by close observation alone. 



The attention of our younger mineralogists should be partic- 

 ularly called to the value of a full description of the associations 

 of minerals. The selected specimens in our cabinets, from which 



It is the rough masses in their natural home, interpenetrated by 

 more recent minerals, or occurring in veins in those which are 

 older, which, with their products of'decom.josition, are most worthy 

 of study, both macroscopicallv and microscopically. A study of 

 mineralogical development mav fimillv lead to a new basis of 

 classification, such as has aireadv been attempted in lithology. 



A Mountain- of Martite.— An iron mountai 



in, the Cerro de 



Mercedo, which rises abruptly out of the plain 



near the city of 



Durango, Mexico, and which, a mile in length, 



is so covered by 



masses of iron ore as to conceal all rock outer- 



ops has been re- 



ported upon by Mr. John Birkenbine, and the ore 



further described 



by Professsor B. Silliman. The ore has the stre; 





tjon of hematite, but the octahedral character 



of the crystals 



showed it to be martite, and it is probable that 



the whole mass 



has been altered from magnetite. 





Analysis of Helvite.— Mr, R. Haines coi 



itributcs to the 



Franklin Institute Journal, a correction of his 



analysis of the 



Helvite, from Amelia Co., Virginia, found by th 



e writer and first 



recorded in the April Naturalist. A re-exa 



mination of the 



specific gravity showed his fust determination to 



have been erron- 





,and. It is now 



found to be 3.29. A new analysis gave total SiO 



,32.49 P er cent 



of which 5.17 per cent, was insoluble in sodic c 



;arbonate, and is 



regarded as gangue. The full analysis was not c 



:ompleted. 



GEOGRAPHY AND TRAVELS 





Proceedings of the Geographical Sec nox , 



)F the British 



Association.— The meeting of the British Associ 



ationforthe Ad- 



vaneement of Science, this year, was held at So 



uthampton, from 



' "file subject of the opening address of the 



president cf the 



Geographical Section, was the Central Plateau of 





e£?S 



ItSfcllI^ 



