OP CREATION. 349 



CHAPTER XV. 



THE CONDITION OP SOUTH AMERICA DURING THE TERTIARY PERIOD. 



I HAVE thought it well to bring to a conclusion the 

 argument derivable from the geology of the old 

 continent and its adjacent islands, because, when we 

 consider the case of South America, to which the 

 present chapter will be exclusively devoted, we find 

 ourselves most emphatically in a new world, and sur- 

 rounded by forms anomalous at first sight, although 

 strictly analogous to the existing fauna of that coun- 

 try, and clearly adapted to its conditions. 



The tertiary geology of South America is on the 

 grandest scale, and of the most instructive nature. 

 Flanked by the great mountain chain of the Andes 

 which runs parallel to the western coast, this country 

 is still the seat of disturbances which ought to be 

 studied as exhibiting the true elements of geological 

 causation and illustrating almost every great geolo- 

 gical principle. That part of the continent extending 

 from the mountains eastward towards the sea is di- 

 vided into vast plains drained by the river Amazon 

 and the Rio de la Plata, and separated by a succes- 

 sion of transverse mountain ridges, comparatively un- 

 important with reference to the subject we have now 

 to consider. 



Almost the whole tract of plain country has been 

 affected by strictly tertiary changes, and elevation has 



