if Ihf Potaro River Ix'low K'aicti'iir Fal 



BRITISH GUIANA AND BRAZIL TO MOUNT RORAIMA 



Bi/ Ihniy E. Craiiijjfon 

 Photographs by the Author 



DnilNC; the past .suiiiiiicr I had tlu- ^oinl fortune to make a journey 

 from Georgetown on the coast of British (iuiana to the great 

 mountain of Roraima — the famous tahU'hmd that stands at the 

 junction of Brazil, \'enezuehi and British Guiana. In its course the way 

 led ah)ng the ri\crsof the lower eotuitry to Kaieteur, the magnificent water- 

 fall of the Potaro ]{i\(r. then eontimied through the higher forests of 

 Guiana across the horder and on.t on the saxannahs of northern Brazil. 



The main olijeet was to run a liiological tra\'erse fi-oin the coast to the 

 high levels centering ahont Mount Roraima. To the biologist, the fauna 

 and flora of this portion of South America are particularly interesting in 

 conn<'ction with the larger problems of ge()grai)hical distribution and 

 evolution, for reasons which may be briefly stated as follows. During the 

 glacial i)erio(l, great ice sheets came well down into the United States and 

 destroyed many or most of the species living there. Later the climatic 

 conditions changed to those of the present temperate sitmition; as such 

 changes gradually came about. North America was repopidated by organ- 

 isms which set out from South .\merica, and mainly from two centers of 

 dispersal. The first of these was the northern Andean region, from which 

 most of the emigrants reached the United States by way of the Isthnuis of 



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