EECREATIVE SCIENCE. 



325 



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THEOEETICAL SECTION OF THE EARTH B CRUST. 



A, Ancient and modem laras ; B, Basalt; C, Porphyry; D, Greenstone ; E, Granite j F, Crystalline schist; 

 G, Silurian; H, Carboniferous ; I, Limestone; K, Red sandstone ; L, Lias; M, Chalk; N, Tertiary; 0, Drift; 

 P, Alluvium; Q, Volcano, communicating with the lowermost Plutonic strata; E, Traps and dykes. 



PHYSICAL EVIDENCES OF THE INTEENAL HEAT OE THE EAETH. 



PAET II. — GEOLOGICAL AND PLANETAET STEUCXTTBE OF THE EAETH. 



HE success which has attended the inves- 

 tigations of Sir Charles Lyell, and the geo- 

 logists generally of the modern school, arises 

 out of the method of reasoning adopted in 

 tracing effects to proximate causes. By what 

 we observe in the changes now taking place 

 on the surface of the earth, we infer the 

 nature of the changes which formed the sue- 

 cessional phenomena of ages long since past, 

 when, truthfully speaking, they were not 

 phenomena, because there was no human eye 

 to behold them. The great Humboldt built 

 up his *' Cosmos" on data collected from the 

 present aspects of Nature, and by the same 

 data we must reason respecting the nature of 

 those fiery forces which have so powerfully 

 operated in giving the habitable globe its pre- 

 Vot. I.— No. 10. 



« 



sent external form and character. That heat 

 was the agent under which the materials of 

 the earth's crust were first modified, is the 

 leading lesson of Geology. If we make a 

 section of the earth's crust, the order of 

 superposition is always the same. From the 

 modern alluvium we proceed downwards to 

 the tertiary, thence to the chalk, the oolite, 

 the new red, the carboniferous, the old red, 

 the Silurian, and at last come upon the sedi- 

 mentary rocks which have been crystallized 

 by heat. Beneath these are the foundation 

 beds of granite, in which there are no traces 

 of the action of water, but abundant evi- 

 dences that they have passed into the solid 

 form, after having been molten for ages. We 

 may find traps, and dykes, and metalliferous 



