FORMATION OF DELTAS. 165 



of the Amazon, in South America, is thus stated by- 

 Mr. Lyell : " A great current flows along the coast 

 of Africa from the south, which, when it reaches 

 the head of the Gulf of Guinea, and is opposed by 

 the waters brought to the same spot by the Guinea 

 current, streams off in a westerly direction, and pur- 

 sues its rapid course quite across the Atlantic to the 

 Continent of South America. Here one portion 

 proceeds along the northern coast of Brazil to the 

 Caribbean Sea and the Gulf of Mexico. Captain 

 Sabine found that this current was running with the 

 astonishing rapidity of four miles an hour where it 

 crosses the stream of the Amazon, which river pre- 

 serves part of its original impulse, and has its waters 

 not wholly mingled with those of the ocean at the 

 distance of 300 miles from its mouth. The sedi- 

 ment of the Amazon is thus constantly carried to 

 the northwest as far as the mouths of the Oronoco, 

 and an immense tract of swamp is formed along the 

 coast of Guiana, with a long range of muddy shoals 

 bordering the marshes, and becoming converted into 

 land. The sediment of the Oronoco is partly de- 

 tained and settles near its mouth, causing the shores 

 of Trinidad to extend rapidly, and is partly swept 

 away by the Guiana current into the Caribbean Sea. 

 According to Humboldt, much sediment is carried 

 again out of the Caribbean Sea into the Gulf of 

 Mexico. The rivers also, which descend from the 

 high platform of Mexico, between the mouths of 

 the Norte and Tampico, where they arrive swollen 

 by tropical rains at the edge of that platform, bear 

 down an enormous quantity of rock and mud to the 

 sea; but the current setting across their mouths 

 prevents the growth of deltas, and preserves an al- 

 most uniform curve in that line of coast." In this 

 manner we may account for the existence of those 

 numerous islands in the Caribbean Sea. 



Such are a few of the facts connected with the 

 deposite of those materials which have been deri- 



