22 



EARTH FEATURES AND THEIR MEANING 



and though some occur in meteorites which are not known from 

 the earth, yet of those which are common to both bodies there is 

 agreement, even to the minor details (Fig. 9). It is found, how- 

 ever, that the commonest of the minerals in the earth's shell are 

 absent from meteorites, as the commoner constituents of meteor- 

 ites are wanting in the earth's crust. This observation would go 

 far to show that we may in the two cases be examining different 

 Terresrr/0/ 



0/iaf rarer Terresrria/ ffocte. 



FIG. 9. Diagram to show how terrestrial rocks grade into those of the meteorites- 

 1, oxygen; 2, silicon; 3, aluminium; 4, alkali metals; 5, alkaline earth metals; 

 6, iron, nickel, cobalt, etc. ; a, granites and rhyolites ; 6, syenites and trachytes ; 

 c, diorites and andesites ; d, gabbros and basalts ; e, ultra-basic rocks ; /, basic 

 inclosures in basalt, etc. ; g, iron basalts of west Greenland ; h, iron masses of 

 Ovif ak, west Greenland ; a'-d', meteorites in order of density (after Judd) . 



portions of quite similar bodies ; and this view is strikingly con- 

 firmed when the rocks of the two groups are arranged in the order 

 of their densities (Fig. 9). 



In a broad way, density, structure, and chemical composition 

 are all similarly involved in the gradations illustrated by the 

 diagram ; and it is significant that while there are terrestrial rocks 

 not represented by meteorites, the densest and the most unusual 

 of the terrestrial rocks are chemically almost identical with the 

 less dense of the celestial bodies. 



