COSMICAL GEOLOGY. 165 



limited. Quartz, orthoclase, felspar, mica, hornblende, leucite, 

 nepheline, garnet, and all hydrous silicates are absent, whereas 

 very few of the minerals which have been recognised in 

 meteorites are not known in the earth. 



In the latter part of this century, thin sections of meteorites 

 have been examined microscopically, and it has been shown 

 that there is more structural difference between the terrestrial 

 and meteoric rock than had been supposed from macroscopic 

 examination. Meteorites are in many cases composed of 

 radiating spherical bodies (chondrites) or irregular fragments ; 

 the rent character, the paucity of steam vesicles, and the 

 absence of liquid contents give to microscopic slides of 

 meteorites an unfamiliar appearance, and seem to indicate 

 that they have taken origin independently of the action of 

 water and vapour. 



The classification of meteorites is a very vexed question, 

 some authorities placing more value upon chemical and 

 mineralogical distinctions, and others upon structural distinc- 

 tions. Partsch in 1843 distinguished two main groups stone 

 meteorites and iron meteorites. Reichenbach rejected these 

 groups as too broad, and classified meteorites in nine 

 groups according to physical character, especially the colour 

 and the mineral contents. Gustav Rose, who was Professor of 

 Mineralogy in Berlin University, supported the earlier classifica- 

 tion of Partsch, but arranged sub-groups upon a mineralogical 

 basis. Daubree, the French physicist, in 1867 distinguished 

 meteorites containing iron or Siderites, from Asiderites or 

 meteorites without iron, and sub-divided these again. 

 Meunier accepted Daubree's main groups, but erected a 

 very large number of sub-groups. In England, the meteor- 

 ites represented in the Collection of the British Museum 

 were arranged in three groups according to Story-Maskelyne's 

 classification in 1870-71: (i) Siderites (meteoric iron), (2) 

 Siderolites (meteoric stones containing iron), and (3) Aerolites 

 (meteoric stones without iron). 



The study of meteorites, as Daubree remarks, touches 

 several of the fundamental questions in the history of the 

 universe. They are the only specimens of non-terrestrial or 

 cosmic bodies which we have an opportunity of investigating, 

 and which can yield an insight into the constitution of those 

 masses occupying the vault of heaven. The number of 

 accredited falls of meteorites does not exceed a thousand, and 



