258 



THE GEOLOGIST. 



spoken in a preceding number of The Geologist (vol. ii. p. 85). A 

 first analysis gave tliem "10 per cent, of magnetic substances (iron 

 and iron-oxide) ; 1.70 of chrome-iron, 5.70 of protosulphuret of iron, 

 48 i^er cent, of silicates soluble in acids, and consisting principally of 

 peridote ; 17 per cent, of silicates insoluble in acids, and consisting 

 principally of feldspar and amphibolite." They then proceeded to 

 analyse, with more care, that part of the aerolite which is insoluble in 

 nitric and hydrochloric acids ; and the result is as follows : — 



Silica 56.613 



Alumina 6.653 



Magnesia 19.447 



. Lime 4.012 



Protoxide of iron 9.212 



Oxides of nickel and manganese . . . . 1.100 



Soda 2.128 



Potash 0.398 



99.563 



Berzelius, Rammelsberg, and other chemists who have occupied 

 themselves with this sort of analysis, have already remarked that 

 the composition of the silicates which are insoluble in acids does not 

 coincide with that of any one known mineral. Thus, from the above 

 analysis, it is impossible to write down any chemical formula, as the 

 oxygen of the silica is not proportionate with that of the different 

 bases. This circumstance shows that the insoluble residue is not 

 composed of one silicate only, but of a mixture. Rammelsberg has 

 shown that the simultaneous existence of alumina and alcalies in such 

 a case indicates the presence of feldspathic minerals. He found, as 

 we have before noticed, that in some meteorites this residue coin- 

 cided exactly with the composition of hornblende or augite, according 

 as the alcalies were attributed to labradorite or to oligoclase. It is 

 impossible, in the absence of distinctive crystalline forms, to prefer 

 one of these hypotheses to the other ; each is equally good. 



Following M. Rammelsberg's method, MM. Chancel and Montessier 

 conclude that the soluble portion of the silicates in the aerolite of 

 Montrejeau represents labradorite, and the insoluble portion horn- 

 blende ; or, if the soluble part be made to represent oligoclase, the 

 insoluble portion becomes augite. Hence the mineralogical composi- 

 tion of this remarkable aerolite may be thus represented : — 



Magnetic portion (iron and oxide of iron) . 10.04 



Chrome-iron 0.67 



Proto-sulphui-et of iron 5.72 



Peridote 45.08 



Labradorite = 8.34) / 10.99 = Oligoclase 



Hornblendes 29.17 j | 26.59 = Augite. 



99.02 



