NATURAL AREAS AND REGIONS 



649 



3, THE GUIANAS 



By William Beebe and H. A. Gleason 



I. Physiography and Vegetation 

 (W. B.) 



In their physiography the three 

 Guianas present certain common char- 

 acteristics. The principal features are 

 the rivers and their branch streams. 

 In each colony the northern portion of 

 its area consists of a fluviomarine 

 deposit extending inland and gradually 

 rising to a height of 10 to 15 ft. above 

 the sea. 



Part of the low, coastal land, of 

 these colonies is actually below sea- 

 level. The Atlantic, along shore, is 

 heavy with yellow silt drifted north 

 from the Amazon. This alluvial plain 

 varies in width from 50 to 18 m. and is 

 traversed by ridges of sand and shells, 

 roughly parallel to what is now the 

 coast, indicating the trend of former 

 shore lines. By the draining and diking 

 of these lands the plantations have been 

 developed along the coast and up the 

 rivers. These low lands are attached 

 to a second belt of somewhat higher 

 plateau, which towards the coast is 

 traversed by numerous huge sand- 

 dunes and inland by ranges of hills rising 

 in places to as much as 2000 ft. The 

 greater part of this belt of country, in 

 which the auriferous districts principally 

 occur, is covered with a dense growth 

 of rain forest, increasing in density and 

 elevation until the magnificent height 

 of two hundred feet is attained. It is 

 in this area that considerable and rich 

 gold and diamond deposits are located. 

 There is the savanna region, isolated 

 outliers of the great Brazilian savannas, 

 occurring irregularly and far in the 

 interior growing only a long wiry grass 

 and poor shrubs. The hinterlands 

 consist of undulating open savannas 

 rising into hills and mountains, some 

 grass-covered, some with dense forests. 



The three colonies are sufficiently 

 near alike that detailed description of 

 only one is necessary. Because of the 

 large amount of research which has 

 been done in British Guiana, it is chosen 

 for this purpose. 



II. British Guiana 



TOPOGRAPHY AND CLIMATE 



British Guiana, the westernmost of 

 the three Guianas, has an area of about 

 90,000 sq. mi., lying between latitude 

 1° and 8° N. and longitude 57° and 61° 

 W., with a coast line of 270 mi. The 

 coastal lowlands have a width of 10 

 to 40 mi. along the Atlantic, and are 

 composed of marine alluvium scarcely 

 above sea-level. South of this strip 

 lies a belt of low hills of sand and clay, 

 nearly 100 mi. wide at the east, but 

 much narrower at the west. The moun- 

 tain region occupies most of the hinter- 

 land and consists largely of plateaus 

 1000 to 3000 ft. in altitude, surmounted 

 with mountain ranges. The mountains 

 are comparatively low in the east and 

 south, and culminate in the Pakaraima 

 range of the southwest, where Mt. 

 Roraima reaches an altitude of about 

 8600 ft. 



The Corentyn, Berbice, Demerara, 

 and Essequibo rivers, with their minor 

 tributaries, flow in a generally northerly 

 direction to the Atlantic, which they 

 enter through broad estuaries. The 

 latter receives two large affluents, the 

 Mazaruni and the Cuyuni, which rise 

 on the north slope of the Pakaraima 

 mountains and maintain a generally 

 easterly course. Several rivers of the 

 Northwest district show a strong devia- 

 tion of their courses to the west, due to 

 the gradual deposition of marine allu- 

 vium. All the streams are obstructed 

 by rapids and waterfalls where they 

 pass from one physiographic region to 

 another. Of these Kaieteur is note- 

 worthy for its height of 741 ft. 



The temperature is continuously hot, 

 the monthly variation on the coast 

 being only 3°, and the annual mean 

 about 80°. Maximum temperatures on 

 the coast seldom reach 90°, but in the 

 savanna region the mean maximum 

 exceeds 90°. The average temperature 

 in the sun exceeds 140°. 



There are four seasons, the short dry, 

 February, March, and April; the long 

 wet, May, June and July; the long dry, 

 August, September, October and No- 



