51,6 Scientific Geology. 



Theory of Central Heat. 



The logical mind that adopts these views of the origin of the un- 

 stratified rocks,is irresistibly led to inquire into the commencement and 

 present state of the internal heat which has produced such mighty ef- 

 fects. As to the condition of the globe when this powerful agent 

 began to modify its crust, little more than conjecture can guide our 

 inquiries. Astronomical observations render it probable that the sur- 

 face of the moon is composed almost entirely of volcanic matter ; and 

 that that planet is gradually cooling and passing into a habitable from 

 a choatic state. Comets also, appear to be in a condition still more 

 chaostic ; the matter of which they are composed being actually in 

 some instances expanded into vapor, in consequence of internal heat. 

 The speculative geologist inquires, whethersuch might not have been 

 the early condition of our globe ; and whether it has not been grad- 

 ually cooling from the beginning to the present time : while such 

 animals have been successively placed upon it as possesed natures 

 adapted to its different temperatures. That its surface must have been 

 torn and ravaged by the most powerful volcanic agency in early times, 

 those who admit the igneous origin of the unstratified rocks must 

 allow : and that its temperature has been sinking, is rendered extreme- 

 ly probable by the almost universal occurrence of animals of a topic- 

 al character in the fossiliferous strata of high latitudes. 



The surface of the globe has probably nearly or quite reached its 

 maximum of refrigeration, as several facts seem to prove. But what 

 is the present temperature of its internal parts ? A great number of 

 observations made within a few years in different parts of the world, 

 in mines and other deep excavations, have brought to light the inter- 

 esting fact, that the temperature increases rapidly as we descend into 

 the earth ; indicating even, that at a depth less than 100 miles, a heat 

 exists great enough to fuse all known rocks ; and consequently, that 

 the great mass of the globe beneath this envelope, may now be a mol- 

 ten incandescent mass. Startling as such a conclusion may be, to one 

 who is not conversant with the details and reasonings of geology, it 

 seems to receive confirmation from the occasional ejection of just such 

 melted matter as the theory supposes, from more than 200 volcanoes, 

 which seem to form the safety valves of the vast furnace. And 

 then, still more numerous extinct volcanoes testify to the more pow- 

 erful operation of this agency in former days. The facility too with 



