AEROLITES. 119 



a loud noise though considerably heated, are not incan- 

 descent. They exhibit, on the whole, a general unmislakeable 

 resemblance to one another in their external form, in the 

 nature of their crust, and in the chemical composition of their 

 principal constituents ; and this resemblance is traceable when 

 and wherever they have been collected, at all periods of time, 

 and in all parts of the earth. But this remarkable and early 

 recognised similarity of general character in solid meteoric 

 masses, suffers many exceptions in detail. How different are 

 the very malleable masses of iron from Hradschina in the dis- 

 trict of A gram, or those from the banks of the Sisim in the 

 Jeniseisk government, mentioned by Pallas, or those 

 which I brought from Mexico ( 79 ), all of which con- 

 tain 96 per cent, of iron, from the aerolite of Sienna, which 

 hardly contains two per cent, of iron, from the earthy me- 

 teoric stone of Alais in the Departement du Card, which 

 falls to pieces when immersed in water, and from those of 

 Jonzac and Juvenas, which are without any metallic iron, 

 and are composed of various crystalline ingredients. 

 These diversities have led to the division of the cosmical 

 masses under consideration into two classes; nickelife- 

 rous meteoric iron, and fine or coarse-grained meteoric 

 stones. The crust of these masses, which is only a few 

 tenths of a line in thickness, is very characteristic ; it has 

 often a pitchy lustre ( 80 ) and is sometimes veined. The only 

 instance which I know of the absence of this crust is in the 

 meteoric stone of Chantonnay in La Vendee, which is 

 marked by another circumstance equally rare, viz. the presence 

 of pores and vesicular cavities, like the meteoric stone of Juve- 

 nas. The separation of the black crust from the light gray 



