PREFACE. ix 



of South America are still current, even among men 

 of science. 



I make no pretension to add anything of importance 

 to our store of positive knowledge respecting the 

 region described in this volume ; I shall be content if 

 it should be found that I have suggested trains of 

 thought that may lead others to valuable results. I 

 venture, indeed, to believe that the argument adduced 

 in the sixth chapter, as to the great extent and im- 

 portance of the ancient mountains of Brazil, approaches 

 near to demonstration, and that the recognition of its 

 validity will be found to throw fresh light on the 

 history of organic life in that region of the globe. 



In the Appendices to this volume two subjects of a 

 somewhat technical character, not likely to interest 

 the general reader, are separately discussed. With 

 regard to both of them, my aim has been to show that 

 the opinions now current amongst men of science do 

 not rest upon adequate evidence, and that we need 

 further knowledge of the phenomena, discoverable by 

 observation, before we can safely arrive at positive 

 conclusions. 



In deference to the prejudices of English readers, 

 which are unfortunately shared by many scientific 

 writers, the ordinary British standards of measure and 

 weight have been followed throughout the text, as 

 well as the antiquated custom of denoting temperature 

 by the scale of Fahrenheit's thermometer. With 

 regard to the metrical system of measures and weights, 

 I am fully aware of its imperfections, and if the 



