409 



eruption enters immediately into contact with 

 the atmospheric air ; but it is not here my pur- 

 pose to discuss this great theoretic question. 



After having examined the general structure 

 of South America according to considerations 

 of comparative geognosy, I shall now state sepa- 

 rately the different systems of mountains and 

 plains, of which the mutual connection has so 

 powerful an influence on the state of industry 

 and commerce of the nations of the New Con- 

 tinent. I shall give only a general view of the 

 systems placed beyond the limits of the region 

 which forms the special object of this memoir. 

 Geology being essentially founded on the study 

 of the relations of juxta-position and place, I 

 could not treat of the chains of the shore and of 

 Parime separately, without touching on the other 

 systems placed south and west of Venezuela. 



A. Systems of Mountains. 



«, Cordilleras of the Andes. This is the 

 most continued, the longest, the most constant 

 in its direction from south to north, and north- 

 north-west, of any chain of the globe. It ap- 

 proaches the north and south poles at unequal 

 distances of from 22° to 33°. Its develope- 

 ment is from 2800 to 3000 leagues, (20 to a de- 

 gree,) a length equal to the distance from Cape 

 Finisterre in Galicia to the north-east Cape 

 (Tschuktscfaoi-Noss)ofAsia. Somewhatless than 



