218 The Geology of the Gold Fields of British Guiana. 



COMPOSITIONS OF THE DRIED FINE SOILS Continued. 



The soils which have lieen derived from the basic rocks difl'er from 

 those formed from the granitic and gneissose rocks by the very high 

 proportions of iron peroxide and alumina they contain. Their plij^sical 

 textures are veiy well adapted for cultivation. Whilst they contain 

 fair proportions of nitrogen their contents of potash and phosphoric 

 acid are somewhat low. They are more readily cultivated than are 

 the soils from the acidic rocks, and their higher retentive powers 

 for water render them far less likely to be adversely affected by 

 drought. But it is necessary when planting on these soils not to 

 entirely remove the forest vegetation with which they are naturally 

 covered, as their texture renders tliem, when exposed, very subject to 

 losses by rainwash. Hills and hill sides covered with these soils, if 

 exposed to the tropical rains witliout any protective vegetable 

 covering, are in a comparatively short time converted into liarren areas 

 of ironstone gravel by rainwash. 



The aboriginal Indians usually select the soils deri\-e(.l from the 

 basic rocks for their fields, leaving those from the acidic rocks to their 

 natural destination of suppf)rts for forest trees. But the Indians 

 seldom, if ever, cultivate theii- fields for longer than two oi' three 

 years in succession ; they then either totally abandon them, or, after 

 leaving them to rest for several 3'^ears, during which the land rapidly 

 becomes covered with low scrub, again clear them and obtain one 

 or more crops. Their mode of agriculture on these soils is to clear the 

 area which they intend to plant, felling the trees and burning the 

 brushwood, etc. They distribute the ashes thus o})tained over the 

 land in little heaps, and in or near these heaps they plant cassava- 

 sticks, banana suckers, sweet potatoes, yams, si^gar-cane, maize, etc. 

 During the first season these jdeld satisfactory crops. After the 

 first crops have been reaped the Indians again fertilise the land with 

 the ashes of such brushwood as they are able to readily and easily 

 obtain, but as in the second and succeeding years ashes will not be 

 available in anything like the quantity the}' were the first year the 

 later crops fall ofi' in quantity, whilst after two or three crops there 

 is seldom brushwood, etc., left unljurnt to supply sufiiciei\t of the ash 

 constituents for further crops. 



