8 AMAZONIA AND LA PLATA. 



Towards the east, that is, in British Guiana, few of the peaks and terraces 

 exceed 3,000 feet. But despite their moderate elevation these mountains present 

 an imposing aspect, thanks to their sandstone walls rising hundreds of yards ver- 

 tically above the surrounding plains, their bare white cliffs forming a striking 

 background to the tropical vegetation which clothes the talus accumulated at their 

 base. 



Roraima is continued north-eastwards in the direction of the Mazaruni river 

 by other quadrangular masses, which present the appearance of citadels raised by 

 the hand of man. The regular disposition of the upper strata, level as the surface 

 of the marine waters in which they were deposited, recalls the geological epoch 

 when the now deeply eroded face of the land presented the aspect of a vast uniform 

 plain unbroken by a single undulation of the surface. 



The Pacaraima Mountains. 



Carved by the running w'aters into distinct sections, trending for the most part 

 north-west and south-east, the Pacaraima (" Basket '') Mountains gradually con- 

 tract in the direction of the east. Here they terminate on the banks of the 

 Essequibo in a bold diorite bluff resembling a calabash, whence its Indian name, 

 Camuti. The unfossiliferous sandstone range is pierced here and there by other 

 diorite masses. In the depths of the surrounding forests is occasionally heard a 

 loud noise like a long peal of thunder, which may probably be caused by portions 

 of the vertical cliffs from time to time giving way and falling with a crash.* 



South of these mountains, which are the highest on the Guiana slope of the 

 Atlantic, follow other less elevated masses rising in the middle of the savannas, 

 which appear to have at one time formed the bed of a vast inland sea disposed in 

 a line parallel with the neighbouring oceanic waters. Canucu, Cumucumu, Cora- 

 tamung, and the other isolated groups, which have a mean altitude of about 2,000 

 feet, formerly constituted a chain of crystalline schist or gneiss islands disposed in 

 the same direction as the Pacaraima range. 



Farther south other ridges of like formation run east and west between the 

 Essequibo and the copious Takutu affluent of the Rio Branco. These eminences 

 rise above alluvial lands, which at some remote epoch were also flooded by lacus- 

 trine waters. In several places the parting line between the Atlantic and 

 Amazonian basins is indicated by no perceptible rising ground, and, according to 

 Brown, this lovv-lying divide has an absolute elevation of not more than 348 or 

 350 feet. One of its depressions is flooded by the little Lake Amuku, Avhich lies 

 on the zone of separation between the Pirara, a sub-affluent of the Takutu, and the 

 Rupununi tributary of the Essequibo. Hence in this region of savannas the 

 passage from one slope to the other is extremely easy, and has been followed at 

 all times by the Indian tribes in their migrations between the Amazonian and 

 Atlantic watersheds. 



The absence of natural frontiers between the Essequibo and Amazons basins 



* Charles Barrington Brown, Canoe and Cump Life in British Guiana. 



