the theory of motion. If, as I believe, we are justified in re- 

 garding the revolving meteor-asteroids (aerolites) as portions 

 of our planetary system, their fall upon the earth constitutes 

 the sole means by which we are brought in contact with 

 cosmical substances of a recognizable heterogeneity.* I here 

 refer to the cause which has hitherto rendered terrestrial 

 phenomena less amenable to th rules of mathematical de- 

 duction than those mutually disturbing and readjusting move- 

 ments of the cosmical bodies, in which the fundamental force 

 of homogeneous matter is alone manifested. 



I have endeavored, in my delineation of the earth, to ar- 

 range natural phenomena in such a manner as to indicate 

 their causal connection. In describing our terrestrial sphere, 

 I have considered its form, mean density, electro-magnetic 

 currents, the processes of polar light, and the gradations ac- 

 cording to which heat increases with the increase of depth. 

 The reaction of the planet's interior on its outer crust im- 

 plies the existence of volcanic activity ; of more or less con- 

 tracted circles of waves of commotion (earthquake waves), 

 and their effects, which are not always purely dynamic ; and 

 of the eruptions of gas, of mud, and of thermal springs. The 

 upheaval of fire-erupting mountains must be regarded as the 

 highest demonstration of the inner terrestrial forces. We 

 have therefore depicted volcanoes, both central and chain 

 formations, as generative no less than as destructive agents, 

 and as constantly forming before our eyes, for the most part, 

 periodic rocks (rocks of eruption) ; we have likewise shown, 

 in contrast with this formation, how sedimentary rocks are 

 in the course of precipitation from fluids, which hold their 

 minutest particles in solution or suspension. Such a com- 

 parison of matter still in the act of development and solidi- 

 fication with that already consolidated in the form of strata 

 of the earth's crust, leads us to the distinction of geognostic 

 epochs, and to a more certain determination of the chronolog- 

 ical succession of those formations in which lie entombed ex- 

 tinct genera of animals and plants the fauna and flora of a 

 former world, whose ages are revealed by the order in which 

 they occur. The origin, ransformation, and upheaval of ter- 

 restrial strata, exert, at certain epochs, an alternating actior 

 on all the special characteristics of the physical configura 

 tion of the earth's surface ; influencing the distribution of 

 fluids and solids, and the extension and articulation of con 



Cotmos, vol. i. (Harper's edit.), p 33-65, 136. 



