PRE- TERRES TRIA L HIS TOR V OF ME TEORI TES 6 3 I 



this matter may be iron and other metals. The alternative sup- 

 position is that the matter of the interior may be like that of the 

 crust but has become denser through condensation and pressure. 



The free silica of the earth's crust is readily accounted for 

 if we remember that the rocks of the earth's crust have been 

 worked over, while in meteorites they are seen in their primitive 

 condition. When silicates are exposed to the action of carbonic 

 acid for any length of time the bases change to carbonates and 

 silica is set free.^ It seems reasonable to suppose that the vast 

 amount of calcium and magnesium now held as limestone was 

 originally in the form of silicates. If the carbonic acid of the 

 limestones should be withdrawn to the atmosphere, and their 

 bases combine with the excess of silica of the crust, rocks as 

 basic as those of meteorites would probably be formed. 



Similarly, the lack of oxygen in meteorites may be only 

 relative, and because much of the matter of which they are 

 composed was in the interior, deep-seated and protected from 

 gaseous action. The superficial, lighter siliceous portions of 

 meteorites are found to be oxidized. It is reasonable to believe 

 the earth's substance is not oxidized except for its superficial 

 crust. It may be urged in support of the view that oxygen 

 could not have been present where meteorites were formed that 

 little or no oxygen is found among the free gases obtained from 

 meteorites. But rocks do not seem to have the power of absorb- 

 ing and holding oxygen as they do other gases. Terrestrial 

 rocks do not contain it, although they hold hydrogen, carbon 

 dioxide, and carbon monoxide in large quantities.^ Yet there is 

 no lack of oxygen in the earth's atmosphere. 



The absence of water from meteorites is an important gap 

 in the parallelism of constitution of meteorites with that of the 

 earth. In the gases hydrogen and oxygen, which it has been 

 shown meteorites possess, a cosmic body has the elements neces- 

 sary for the formation of water. Conditions of nascence, or 

 possibly of electricity, might exist in a body the size of the 



'This fact is more fully stated by SiR John Murray, Proc. Roy. Soc. of Edin- 

 burgh, i8go-i, p. 229. 



^ See Studies, Jour. Geol., Vol. IX, p. 402. 



