If the country north of Natchez is alluvial, no one will doubt it is so from this place to the Gulf of Mexico. At Baton Rouge, one hundred and forty miles north of New Orleans, you meet the first elevated land in ascending from the gulf. The banks of the Mississippi are higher than the interior, and would be annually overflowed by the river, but for a narrow embankment of earth about six feet high, called the Levee. By means of this, a narrow strip of land, from half a mile to a mile in width, is redeemed, and cultivated with cotton and the sugar cane, to the great advantage of the planter. Generally, within one mile from the river, there is an impenetrable morass. The country has every where the appearance of an origin comparatively recent. Not a rock on which you can stand, and no mountain to gladden the eye; you seem to have left the older parts of creation to witness the encroachments which the earth is continually making upon the empire of the sea; and on arriving at the mouth of the Mississippi, you find the grand instruments of nature in active operation, producing with slow, but certain gradations, the same results. _A destructive Insect._ But I will not enlarge on a fact already familiar. I will ask your further indulgence only, while I communicate an authentic and curious fact for the information of the zoologist. In the Choctaw country, one hundred and thirty miles northeast of Natchez, a part of the public road is rendered famous on account of the periodical return of a poisonous and destructive fly. Contrary to the custom of other insects, it always _appears_ when the _cold weather_ commences in December, and as invariably _disappears_ on the approach of _warm weather_, which is about the first of April. It is said to have been remarked first in the winter of 1807, _during a snowstorm_; when its effects upon cattle and horses were observed to be similar to those of the gnat and musqueto, in summer, except that they were more severe. It continued to return at the same season of the year, without producing extensive mischief, until the winter of 1816, when it began to be generally fatal to the horses of travellers. So far as I recollect, it was stated, that from thirty to forty travelling horses were destroyed during this winter. The consequences were alarming. In the wilderness, where a man's horse is his chief dependence, the traveller was surprised and distressed to see the beast sicken and die in convulsions, sometimes within three hours after encountering this little insect. Or if the animal were fortunate enough to live, a sickness followed, commonly attended with the sudden and entire shedding of the hair, which rendered the brute unfit for use. Unwilling to believe that effects so dreadful could be produced by a cause apparently trifling, travellers began to suspect that the Indians, or others, of whom they obtained food for their horses, had, for some base and selfish end, mingled poison with it. The