ON THE 



STRUCTURE, AND MODE OF ACTION 



OF 



VOLCANOS, 



,>! v.. 



IN DIFFERENT PARTS OF THE GLOBE. 



[This dissertation was read in a public assembly of the Academy at Berlin, 

 on the 24th of January, 1823.] 



WHEN we reflect on the influence which, for some centuries past ;- 

 the progress of geography and the multiplication of distant voyages 

 and travels have exercised on the study of nature, we are not long 

 in perceiving how different this influence has been, according as the 

 researches were directed to organic forms on the one hand, or on the 

 other to the study of the inanimate substances* of which the earth is 

 composed to the knowledge of rocks, their relative ages, and their 

 origin. Different forms of plants and animals enliven the surface 

 of the earth in every zone, whether the temperature of the atmo- 

 sphere varies in accordance with the latitude and with the many 

 inflections of the isothermal lines on plains but little raised above 

 the level of the sea, or whether it changes rapidly in ascending in 

 an almost vertical direction the steep declivities of mountain-chains/ 

 Organic nature gives to each zone of the earth a peculiar physiog- 

 nomy; but where the solid crust of the earth appears unclothed by 

 vegetation, inorganic nature imparts no such distinctive character. 

 The same kinds of rocks, associated in groups, appear in either 



