IVTRODUCTION. 45 



domes of trachyte, and cones of basalt, by the elastic forces 

 emanating from the fluid iiiterior of our globe, has led one 

 of the first geologists of the age, Leopold von Buch, to the 

 theory of the elevation of continents, and of mcuntain chains 

 generally. This action of subterranean forces in breaking 

 through and elevating strata of sedimentary rocks, of which 

 the coa&t of Chili, in consequence of a great earthquake, fur- 

 nished a recent example, leads to the assumption that the 

 pelagic shells found by M. Bonpland and myself on the ridge 

 of the Andes, at an elevation of more than 15,000 English 

 feet, may have been conveyed to so extraordinary a position, 

 not by a rising of the ocean, but by the agency of volcanic 

 forces capable of elevating into ridges the softened crust of 

 the earth. 



I apply the term volcanic, in the widest sense of the Avord, 

 to every action exercised by the interior of a planet on its 

 external crust. The surface of our globe, and that of the 

 moon, manifest traces of this action, which in the former, at 

 least, has varied during the course of ages. Those who are 

 ignorant of the fact that the internal heat of the earth in- 

 creases so rapidly Avith the increase of depth that granite is 

 ui a state effusion about twenty or thirty geographical miles 

 belovv' the surflice,* can not have a clear conception of the 

 causes, and the simultaneous occurrence of volcanic eruptions 

 at places widely removed from one another, or of the extent 

 and intersection of circles of commotion in earthquakes, or of 

 the uniformity of temperature, and equality of chemical com- 

 position observed in thermal springs during a long course of 

 years. The quantity of heat peculiar to a planet is, however, 

 a matter of such importance — being the result of its primitive 

 condensation, and varying according to the nature and dura- 

 tion of the radiation — that the study of this subject may 

 throw some degree of light on the history of the atmosphere, 

 and the distribution of the organic bodies imbedded in the 

 Eolid crust of the earth. This study enables us to understand 

 how a tropical temperature, independent of latitude (that is, 

 of the distance from the poles), may have been produced by 

 deep fissures remaining open, and exhaling heat from the in- 



* The determinations usually given of the point of fusion are iu 

 general much too high for refracting substances. According to the very 

 iiccurate researches of Mitscherlich, the melting point of granite can 

 hardly exceed 2372^ F. 



[Dr. Mantell states in The Wonders of Geology, 1818, vol. i., p. 34, 

 diat this increase of temperature amounts 'o 1 '' A Fahrenheit for evei-y 

 fifty-four feet of vertical depth .] — Tr. 



