CHAP. XXIX.] RTVER FOGS. 113 



miles in southern steamboats, since leaving South Carolina, with 

 out a mischance, I might have looked on this adventure as very 

 ominous. 



The greater part of New Orleans would be annually over- 

 flowed by the river, but for the &quot; levee,&quot; an artificial embank 

 ment, eight or nine feet high, which protects the city. This 

 levee became less and less elevated as we descended the stream. 

 We saw the buildings of several sugar plantations just behind it, at 

 a short distance from the edge of the bank. When we had gone 

 about twenty miles, below the bend called the English turn, I 

 was struck with the resemblance of the Mississippi to the Savan 

 nah, Alabama, and Altamaha rivers, where they flow through 

 a broad alluvial plain, with no bluffs in sight. The swamps on 

 both sides, although several feet lower than the river banks, have 

 the aspect, as before stated, of wooded eminences. 



The distance from New Orleans to the great pilot-station at 

 the mouth of the river, called the Balize, is about 80 miles by 

 land, and 1 1 by water. We had been told we should reach 

 our destination before night ; but we were scarcely half way, 

 when we cast anchor in a dense fog, followed in the course of 

 the night, by much lightning and rain. We found the tempera 

 ture of the water to be 46 Fahrenheit, while that of the air had 

 varied, in the course of twenty-four hours, from 50 to 75. This 

 difference between the temperature of the water and air, often 

 amounting to 3 Fahrenheit, gives rise to the fogs which prevail 

 at this season. The river flowing from the north, where there is 

 now much ice and snow, is always much colder, and I am in 

 formed by pilots, that as far as the Mississippi water can be 

 traced, by its color, into the gulf, it is commonly covered, in the 

 spring, with dense fog, while the atmosphere is clear on each 

 side. These fogs are generated in the same manner as ordinary 

 clouds, by the mixture of two currents of air of different degrees 

 of temperature. The river cools the air in contact with its sur 

 face, and this colder layer of air mingling with the warmer layer 

 immediately over it, causes the fog to begin to form close to the 

 water. Hence it is frequently confined to the bed of the river, 

 not spreading at all over the banks. The upper surface is often 



