290 Fiision- Structures in Meteorites. 



bodies of ex-terrestrial origin that rcacli our globe, including 

 thus meteorites, meteoric iron, and meteoric or cosmical dust. 

 The term "meteorite" is to designate all of such ex-terrestrial 

 bodies as are composed of stony and metallic matter, without 

 regard to the proportions in which these two may respectively 

 occur. "Meteoric iron" is to be limited to that class of aero- 

 lites formed wholly of metal; while "meteoric dust" is to be 

 confined to that portion reaching the globe in a finely divided 

 state. 



The theories that have been advanced to account for the 

 origin of aerolites are quite numerous. They may, however, 

 all be conveniently classed with one or the other of two 

 great divisions, of which the first would claim for them terres- 

 trial sources ; the second, cosmical sources. 



The first may again be divided into — 

 (a.) Volcanic. 

 (1).) Atmosj)heric. 



The latter into — 



{a.) Lunar Volcanic. 



{!).) Planetary. 



(c.) Solar. 



id.) Cometary. 



To discuss these theories in detail, is not within the province 

 of this article ; after a careful consideration of the merits of 

 each, however, my inclination is to accept the so-called planetary 

 theory advanced by Chladni, and which holds that "meteorites 

 are true though minute planetary fragments, created by the 

 impact and disruj)tion of larger cosmical masses." 



Of the many classifications suggested, only Daubree's will be 

 cited. He divides aerolites into — 



SiDEKITES. ASIDEEITES. 



Containing metallic iron. Containing no metallic iron. 



(1.) Holosiderous. (1.) Asiderous. 



Iron or alloys of iron and other 

 metals only. 



