

COMPOSITION OF EARTH 

 ^ 



Fig. 20 1 



Fig. 292 



I'rimitive igneous 

 rock. 



Primitive igneous 

 rock. 



Planetesimal matter 

 predominant; igneous 

 rock abundant; sr.li 

 mentary rock a minor 

 constituent, increasing 

 toward the surface. 



Planetesimal 



matter with 



more or less 



igneous 



rock. 





.?oi. A diagrammatic sector of the earth illustrating its structure accord- 

 ing to UK- Laplacian hypothesis. The great body of the earth is made up of the 

 original igneous rock. Sedimentary rocks, together with some extrusive rocks, 

 nit a thin coating, represented in the diagram by black, outside the great 

 igneous interior. The original igneous rock is represented as appearing at the sur- 

 face in. some places (^i). This, according to one view, might represent the Archean 

 roi k . 



.MI.:. Diagram illustrating the composition of the earth on the modified 

 form of the Laplacian hypothesis. The great body of the earth is the original 

 igneous rock. Outside this original igneous mass, there is a zone (zone 2) of ex- 

 trusive material, with perhaps some sedimentary rock interbedded. The material 

 of tliis /.one is represented as coming to the surface at some points (JR). Outside 

 this /-.one there is a third, made up primarily of sedimentary, but subordinately, of 

 extrusive nwks. The material of the second zone might constitute the Archean 

 rock. 



Fig. .;<)<. Diagram representing the structure of the earth according to the 

 planeteaimal hypothesis. The material of zones i and 2 is indicated in the diagram. 

 /one ; of this figure corresponds to zone 2 of Fig. 292, and zone 4 of this figure corre- 

 .-pondsio the outermost /.one of Figs. 291 and 292. 



