130 Geology of South America. 



to the west of the land already elevated, was the first to as- 

 sume a relief from north to south, thus changing completely 

 the form of the Continent. Subsequently the eruption of the 

 trachytes, and the first outbreak of the now existing volcanoes, 

 completed the external forms of this vast chain, and gave to 

 the shores of the Continent their present configuration ; and 

 it is very remarkable that these last phenomena manifested 

 themselves more especially in the western region of the Con- 

 tinent, where the earthquakes of the present day have concen- 

 trated their action. 



This general remark on the advance of the soulevements 

 from the east to the west, leads to a curious analogy between 

 the New and the Old World. Buifon had already been struck 

 by the diff'erence in the form of the two great Continents. 

 He had remarked that in the Old Continent, or to speak more 

 exactly, in Europe, Asia, and the north of Africa, the great 

 geographical features are arranged in relation to an east and 

 west line, nearly as they are in the New World in relation to 

 a north and south line. Mr Poulet Scrope, in addition to this 

 observation of BufFon, remarked the essential difference pre- 

 sented by the east and west sides of the South American 

 Continent, in that, while the one presents a long ridge brist- 

 ling with peaks and volcanoes, the other exhibits large rounded 

 mountains, without any indication of volcanic phenomena. 

 The results obtained by M. D'Orbigny enable us to charac- 

 terise this analogy more exactly, inasmuch as it appears that in 

 South America the successive soulevements which have fashion- 

 ed the relief of the Continent, had generally their principal 

 point of application more and more to the west in proportion 

 as they are more modern ; whereas in Europe the soulevements^ 

 in proportion as they are more modern, exercised their princi- 

 pal efi'ects more and more to the south. 



In America the great plains of the Pampas and of the Ama- 

 zon, correspond to that great plain in the north of Europe, of 

 which a small depression is occupied by the waters of the 

 Baltic ; and the vast lake of Titicaca fills the sinuosities pro- 

 duced by the meeting of the various systems which cross one 

 another in the Andes, much in the same manner as the Me- 



