COXTEMPOEANEOUS CRYSTALLIZATION OF lEOX AND SILICATES. 115 



bodies — especially concerning the strange lines in the sun's spectrum — it 

 would appear that meteorites ought to be studied more critically than ever 

 for the rarer elements, as well as for some at present unknown. 



Careful examinations ought also to be made on microscopic sections of 

 recently fallen meteorites, in order to ascertain if any changes have taken 

 place in the rock since it was first formed, but before it reached this earth, 

 since all changes now seen in them are referred to the action of our atmos- 

 phere after the fall of the meteorite. It is not to be expected that in 

 any way can any clue be obtained as to how recentlj' or how long ago the 

 meteorite left its parent mass, since no alteration in its substance can be 

 expected to have taken place in inter-solar space. 



Mr. H. C. Sorby's view* that it is impossible for minerals of so diverse 

 specific gravity as iron and olivine to crystallize together in the pallasites 

 and other metallic meteorites on the surface of the earth or any large body, 

 but that they came from the metallic centre of small bodies, or else formed 

 small planets by themselves, does not seem to be well founded. The same 

 method of reasoning would prove that magnetite could not be formed with 

 leucite, or feldspar, or augitc in any lava-flow on the earth's surface ; yet 

 they are minerals of common occurrence together in lavas. Hence it is 

 claimed here that the crystallization of silicates with metallic iron might, so 

 far as gravity is concerned, take place on the surface of the earth as it has 

 been proved to have done in Greenland. So too, if such a structure and 

 arrangement of iron and olivine could not take place on the surface of a body 

 like the earth, then the rocks of Cumberland, Ehode Island, and of Taberg, 

 Sweden, ought not to exist since they have this structure and are at the 

 surface of the earth. The difference between the magnetite and olivine is 

 not so great as that between the native iron and olivine, but yet it is suffi- 

 cient to cause a separation, if Sorby's view is correct. 



Helmholtz's theory that the earth is built out of meteorites is negatived 

 by the following facts : the geological formations in and of themselves are 

 not composed of detached fragments like meteorites ; meteorites, so far as 

 known, are not found in the geological formations; and the chemical com- 

 position of the latter is different from that of the meteorites. His view 

 seems to be a pure theory without any regard being paid to the actual 

 known structure and composition of the earth and meteorites. As well 



* Quart. Jour. Sci., lS6i, i. 717. 



