86 INTRODUCTION. 



sand-hills run several detached groups of hillocks, 

 which in French Cayenne almost approach the 

 sea-coast. A chain of mountains, which I am in- 

 clined to consider the old boundary of the Atlantic 

 (^cean, crosses Guiana in a south-eastern direction, 

 tlirough which tlie large rivers of that district have 

 forced themselves a passage, their course being im- 

 peded by numerous rapids and cataracts. The cul- 

 minating point of this chain, which is connected 

 with the Pacaraima mountains by detached groups, 

 is a range of sand-stone mountains, of whicli the 

 highest is called Roraima by the Indians ; its 

 eastern point is in latitude 5 deg. 9 min. 36 sec. 

 north, longitude 60 deg. 47 niin. west. This re- 

 markable mountain group extends twenty-five miles 

 in a north-west and south-east direction, and rises 

 to about 7500 feet above the sea, the upper 1500 

 feet presenting a mural precipice. Down tlie face 

 of these mountains rush numerous cascades, which 

 eventually form tributaries to the three great rivers 

 of Guiana, namely, the Amazon, the Orinoco, and 

 the Essequibo ; and they form, therefore, the se- 

 paration of waters of the basin of the Orinoco and 

 Essequibo on the north, and the Amazon on the 

 south. 



The Sierra Acarai gives rise to some of the largest 

 rivers of Guiana. This mountain chain crosses the 

 axis of that imaginary line of geographers, the equa- 

 tor, and its average height is about 3000 feet. 

 Here the rivers Essequibo, Corentyn, Maroni or 

 Marooini, and several tributaries of the Amazon, 



