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- 
