54 NATURAL HISTORT 



peat-molTes, and they are certainly tinged by the fame caufe. 

 The rotten leaves of trees, and other decayed parts of vegeta- 

 bles on the hills, inftead of being coUecfled on the furface to 

 form foil, are wafhed down into the fandy ftrata by every rain ; 

 fo that the refervoirs of the fprings, and the water which pro- 

 ceeds from them, is always coloured with thefe fubflances. There 

 follows a corollary alfo from this general principle, and when 

 compared with fadls I believe it will hold good : The more the 

 fand is concreted into flone in any of the hills, the more and 

 better will be the foil upon them. Where clay in fmall beds, 

 or in a certain proportion, is mixed with the fand, the vegeta- 

 ble mould will likewife be better retained. 



Rivers. — I will next give you what general obfervations I 

 have been able to make upon the rivers and creeks of this part 

 of America. The courfe of nearly all thofe of Guiana is from 

 fouth to north. They originate in a chain of hills running eafl 

 and weft, which feparates Guiana from the country on the Ama- 

 zons, and likewife gives rife, on its fouth lide, to the numerous 

 branches which fall into that river. The Demerary is a confi- 

 derable ftream, equal, if not fuperior to the Thames ; yet it is 

 by no means among the largeft of them. The Elfequebo is 

 five times larger at its mouth, forming a whole Archipelago of 

 iflands ; but its ftream foon divides, and, on account of rocks, 

 fhallows and rapids, none of its branches are navigable fo high 

 up as the former. Moft of the particulars I am now to give 

 you muft be underftood as applying to the Demerary. The 

 bar, if it may be fo called, is common to this with many other 

 rivers, which difcharge themfelves into a Ihallow fea ; but ftill 

 with circumftances in the prefent cafe which diftinguifti it from 

 others, where the bottom is not mud but fand. It does not run 

 like a fingle narrow ridge, acrofs, or nearly acrofs the mouth 

 of the river, but it is of great extent, and is properly a con- 

 tinuation of the mud-bank which runs all along the coaft. To 

 the eaft and weft, and for two miles or more in the offing, you 



have 



