RocJcs of North Devorif <^c. 127 



oscillations of the isothermal surfaces of great temperature, 

 founded on the assumption of an incandescent mass existing 

 deep below the Surface of the Earth. If we adopt this theory, 

 which appears to afford a fair starting-point, it may not be 

 very difiicult to conceive developments of heat in the bowels 

 of the earth proportionate to the depths of the mineral de- 

 posits and the pressures to which they may have been sub- 

 jected, during the progressive construction of the Shell of the 

 Globe to its present form and state ; but which differed in the 

 degrees according to the conditions that prevailed at different 

 epochs. That a portion of this pressure was due to an in- 

 cumbent ocean cannot admit of doubt, since all mineral forma- 

 tions, from the fundamental granite upward to the most re- 

 cent of the tertiary class, exhibit abundant phaenomena attest- 

 ing this im mergence. 



In all successive epochs, therefore, pending the building up 

 of the Crust of the Earth to its existing form and condition, it 

 may be said that the combined or reacting agencies of heat 

 and water have never been absent; though modified and va- 

 ried in intensity and force according to the circumstances 

 which interfered at given periods. 



Hence it appears that we are not strictly justified in pro- 

 nouncing rock formations, of whatever sera, as of purely igne- 

 ous or of purely aqueous origin ; for as in all cases heat and 

 water have been conjointly or conflictively set in motion, it 

 becomes, in any case, simply a question of the relatively 

 greater or less intensity and energy with which their respective 

 forces have been combined or have reacted on each other ; 

 and as all formations of a date antecedent to the post-diluvial 

 were (if we except the lacustrine) formed adjacent to, in, or 

 under the Ocean, their various conditions of position and 

 structure, both general and subordinate, appear referable 

 primarily to the laws of chemical and molecular attractions, 

 modified by greater or less developments of heat and mecha- 

 nical agency, under the influence of hydrostatic pressure. 



During the progress of the formation of strata in the ocean, 

 and the incidental raisings and subsidences to which they may 

 have been subjected by elemental combinations or conflicts, 

 fractures, disruptions, and dislocations would follow as a con- 

 sequence ; and such movements may, in some of their results, 

 have given rise to the origin of many veins. Hence, a distinc- 

 tion between primary disposition and structure, and successive 

 displacements, appears legitimate; comprehending under the 

 term structure, all crystalline, stratified, and concretionary 

 arrangements of whatever description ; whether slaty, tabular, 

 prismatic, globular, coliunnar, or otherwise. 



