CHAPTER XI 



DISCOURS PRELIMINA1RE, ETC. 



ALL those who have studied attentively the materials of the earth 

 which we inhabit have been forced to recognise that our globe has 

 suffered great revolutions which must have required for their accom- 

 plishment a long series of centuries. Memories of some of these revolu- 

 tions have even been traced in the traditions of early peoples. The 

 philosophers of antiquity exercised their wits in endeavours to ascertain 

 the order and the causes of these vicissitudes ; but, more eager to 

 interpret nature than patient in her study, they relied on inadequate 

 observations and on traditions distorted by poetry and superstition, 

 and thus were led to invent Cosmogonies, or Systems of the Origin 

 of the World, better suited to please the imagination than to satisfy 

 the intellect by a faithful interpretation of nature. 



It was long before it was recognised that this branch of Natural 

 Science, like all others, ought to be pursued with the help of observa- 

 tion, and that systems ought never to be put forward except as the 

 results and the consequences of facts. 



The science which collects the facts that can alone serve as a 

 basis for the Theory of the Earth, or Geology, is Physical Geography, the 

 description of our globe, of its natural divisions, the character, the 

 structure, and the situation of its different parts, of the substances 

 visible on its surface, and of those which it contains in such depths 

 as our feeble resources enable us to penetrate. 



But it is above all through the study of mountains that the progress 

 of a Theory of the Earth can be accelerated. Plains are uniform ; 

 it is impossible in them to inspect a section of the soil and its different 

 beds except by excavations effected either by water or by the hands 

 of men ; and such means are very inadequate, because these excava- 

 tions are of relatively rare occurrence and extent, and the deepest 

 scarcely descend to 1200 or 1800 feet. High mountains, on the other 

 hand, infinitely various in their material and their form, present to 

 the light of day natural sections of a great extent, in which one can 

 observe with the utmost precision, and embrace in a moment, the 

 order, the situation, the direction, the thickness, and even the nature 



1 Voyages dans les Alpes, vols. i. and iv. 



J86 



