184 DELTA OF THE MISSISSIPPI. [CHAP. XXXIV. 



the junction of the Ohio, is of the same character, including, 

 according to Mr. Forshey, an area of about 16,000 square miles, 

 arid is, therefore, larger than the delta. It is very variable in 

 width from east to west, being near its northern extremity, or at 

 the mouth of the Ohio, 50 miles wide, at Memphis 30, at the 

 mouth of the White River 80, and contracting again further 

 south, as at Grand Gulf, to 33 miles. The delta and alluvial 

 plain rise by so gradual a slope from the sea as to attain at the 

 junction of the Ohio (a distance of 800 miles by the river) an 

 elevation of only 200 feet above the Gulf of Mexico. 



First, in regard to the whole alluvial slope, whether above or 

 below the present head of the delta, it will appear, from what has 

 been already said, that sand is thrown down near the borders of 

 the main river and its tributaries, arid fine mud at more distant 

 points. The larger portion, however, of the whole area consists 

 of swamps, supporting a luxuriant growth of timber, interspersed 

 with lakes, most of which are deserted river bends. These lakes 

 are slowly filling up, and every swamp is gradually becoming 

 shallower, the substances accumulated in them being, for the 

 most part, of vegetable origin, unmixed with earthy matter. It 

 is only on their exterior margins (except after a sudden subsidence, 

 daring an earthquake like that of 181112), that the waters of 

 the Mississippi throw down sediment in the interior of any large 

 swamp or lake, for the reeds, canes, and brushwood, through 

 which the waters must first pass, cause them to flow slowly, 

 and to part with all the matter previously held in mechanical 

 suspension. Long before they reach the central parts of a morass 

 or lake, they are well filtered, although still deeply stained by 

 vegetable matter in a state of decomposition. 



Over a large portion of the submerged areas of the great plain, 

 trees are seen growing every where in the water. Into the deeper 

 water, where no forest can grow, the trunks of trees are floated, 

 and many of these sink, when water-logged, to the bottom, which 

 is also raised by an annual deposit of leaves, and of peaty matter 

 derived from decaying plants, of which there is an exuberant 

 growth round the borders of every swamp. That the admixture 

 of inorganic matter is very small, has been shown by the observ- 



