24 AMAZONIA AND LA PLATA. 



current. But the southern section has, on the contrary, been deeply eroded by 

 the marine waters ; a portion of the old shore has been washed away, and the 

 Cape do Norte, as well as Maraca Island, are so many fragments of the ancient 

 continental seaboard. Along the whole length of the coast of Dutch Guiana east 

 and west of Paramaribo, the existence of older beaches may be traced by the lines 

 of snags deposited by the marine current and now embedded in the littoral alluvia. 



Analogous contrasts are presented by the character of the coast streams in 

 both regions. Off the shores of Dutch Guiana the soft mud covering the bed of 

 the sea yields like a movable carpet to the action of the Atlantic billows, and 

 thus tends to diminish their force. Thus the rollers gradually subside until the 

 sea becomes quite smooth, so that vessels often find safe anchorage between the 

 marine current and the shore while the storm rages on the high sea. 



About the Cape do Norte and Maraca Island, on the contrary, the tides rush 

 in with extreme violence. Nowhere else, not even in the Amazonian estuary, 

 does the pororoca, as the bore is locally called, roll up more suddenly, or with a 

 succession of more powerful waves. So far back as 1743 La Condamine had 

 already described the waters about the Araguari estuary as amongst the most 

 dangerous for shipping. The tides, pent up in the narrow gulf on a gradually 

 shoaling bed, rise in a few minutes to one-third of high water level ; they have 

 occasionally been observed to rise almost suddenly as many as 20 or even 26 feet. 

 The floods spread far over the low-lying coastlands, and during the spring tides, 

 when there is a rise of from 40 to 50 feet, whole strips of the mangrove-covered 

 beach have been swept away. These verdant islands, drifting with the current, 

 are stranded farther north about the Cachipour and Oyapok estuaries. Even at 

 neap tide the difference between ebb and flow in these waters is still about 10 

 feet. 



Subjoined is a table of the chief Guiana rivers between the Orinoco and the 

 Amazons, with approximate estimates of their length, areas of drainage, dis- 

 charge, and extent of navigable waters for small steamers : — 



Mean disoliai-jre Length of 



per second in navigab.e 



cubic fe^^t. waterway. 



< 0,000 40 



7,250 94 



18,000 165 



3-5,000 70 



18,000 96 



39,000 46 



2,700 38 



20,000 46 



14,000 50 



7,250 44 



14,000 125 



At a distance of from 15 to 50 miles off the coast flows the great marine 

 current, which sets from Cape S. Roque towards Trinidad. Its axis extends 

 on an average 134 miles from the mainland, and its total breadth may be esti- 

 mated at from 230 to 250 miles. It varies in velocity with the winds, at times 

 exceeding 90 or 95 miles a day, while at others, when retarded by the trade 



