22 AMAZOXIA AND LA PLATA. 



the sandstone, granite, or diorite reefs rising to or above the surface arc covered, 

 as with a coating of tar, by a film composed of iron and manganese oxides. As on 

 the Orinoco, the harder the rock the blacker the film, which in rainy weather emits 

 noxious odours. 



Below the reefs and rapids the broad deep rivers, discoloured and dammed up 

 by the tidal current, roll down a yellowish water often hidden beneath floating 

 vegetation. In their lower reaches these streams merge in the riverside morasses, 

 lakes, or lagoons, which in French Guiana take the name oî jjnpris. In the more 

 settled and better-cultivated districts of the British and Dutch seaboard the 

 direction and discharge of the flood waters have been regulated by dykes and 

 canals. On the plantations sluices are used to arrest the tides, while the percolat- 

 ing waters are discharged at ebb through the so-called kolcers, or ditches. About 

 the estuaries the fresh water of the Guiana rivers floats on the heavier salt water 

 for a distance of six or eight miles seawards. 



The Guiana Lakes. 



Thanks to the uniform slope of the land, the old lakes which formerly studded 

 ihe surface of Guiana, and whose contours may often still be traced in those of 

 the savannas, have nearly all been discharged. These ancient lacustrine depres- 

 sions have been best preserved in the contested Franco-Brazilian territory between 

 the MajDa Grande and Araguari rivers. 



This lake-studded district lies back of the low-lying peninsular headland of 

 Cape do Norte and the equally low island of Maraca. Within a comparatively 

 recent epoch the zone of fresh-water lagoons extended much farther north all the 

 way to the Oyapok river, and at that time all these lakes, creeks, and channels 

 presented a continuous waterway, over 200 miles between Amazonia and French 

 Guiana, navigable throughout by boats and barges. According to the officers in 

 command of the French fort of Mapa, which was maintained during the years 

 1836 — 41, craft of forty tons were still able to follow this route about the middle 

 of the nineteenth century. The Ljgo Grande, immediately south of the Mapa 

 Grande river, is now a mere fragment of the large sheet of water encircling the 

 island on which stood the French fort abandoned in 1841, and reoccupied by the 

 Brazilians in 1890. 



South and south-east of the peninsular Cape do Norte follow other lakes, one 

 of which, Lake Jac, near the Carapaporis Strait between the mainland and Maraca 

 Island, appears to still preserve the form of a spacious baj^ but Avithout shelter, 

 hence exposed to the Atlantic storms^ and scarcely any longer navigable by the 

 native boatmen. 



The Lago Novo, near the Araguari river at the southern extremit}^ of the 

 lacustrine chain, also resembles a marine inlet, and even affords a retreat to 

 manatees, which here browse on the forests of aquatic plants. But it is also acces- 

 sible to barges, which find shelter from the Atlantic gales under the lee of the 

 insular groups which form so many transverse breakwaters. Having a depth of 

 from 30 to 40 feet, this basin might easily be transformed to a magnificent 



