TO STRATIFIED ROCKS 41 



once been in a fluid, or even in a nebular state,* from the pre- 

 sence of intense heat, the passage of the first consolidated 

 portions of this fluid, or nebulous matter, to a solid state 

 may have been produced by the radiation of heat from its 

 surface into space ; the gradual abstraction of such heat 

 would allow the particles of matter to approximate and 

 crystallize ; and the first result of this crystallization might 

 have been the formation of a shell or crust, composed' of 

 oxidated metals and metalloids, constituting various rocks 

 of the granitic series, around an incandescent nucleus, of 

 melted matter, heavier than granite ; such as forms the moi'e 

 weighty substance of basalt and compact lava. 



It is now unnecessary to dwell on controversies which 

 have prevailed during the last half century, respecting the 

 origin of this large and important class of unstratified crys- 

 talline rocks, which the common consent of nearly all mo-, 

 dern geologists and chemists refers to the action of fire. 

 The agency of central heat, and the admission of water to 

 the metalloid bases of the earths and alkalis, ofler two causes 

 which, taken singly or conjointly, seem to explain the pro- 

 duction and state of the mineral ingredients of these rocks; 

 and to account for many of the grand mechanical move- 

 ments that have affected the crust of the globe. 



The gradations are innumerable, which connect the in- 

 finite varieties of granite, syenite, porphyry, greenstone, and 

 basalt with the trachytic porphyries and lavas that are at 

 this day ejected by volcanos. Although there still remain 

 some difficulties to be explained, there is little doubt that 

 the fluid condition in which all unstratified crystalline rocks 



* The nebular hypothesis oTers the most simple, and therefore the most 



probable theory, respecting the first condition of the material elements that 



compose our solar system. Mr. Whewell has shown how far this theory 



supposing it to be established, would tend to exalt our conviction of the 



prior existence of some presiding Intelligence.— Bridjewuter Treatises, No.. 



HI. Chap. vii. 



4* . 



