THE MISSISSIPPI VALLEY. H 



Cairo, at the mouth of the Ohio, is computed to be 1,178 miles from the 

 Gulf of Mexico. The descent of the Mississippi, from the mouth of the Ohio 

 to the Gulf of Mexico, is therefore 2^% inches per mile, at low water. 



From Cairo to Pittsburg the ascent is 424 feet, and the computed distance 

 975 miles. The avei'age inclination of the Ohio is therefore StV/o inches per 

 mile. 



From Pittsburg to Olean Point the ascent is 704 feet, and the computed dis- 

 tance 250 miles. The average inclination is therefore 2 feet 10 inches per mile. 



The distances from point to point along these rivers are not obtained from 

 actual survey, but are the computed distances as they are estimated by watermen, 

 or laid down in the rough charts of the river. While, therefore, we may regard 

 the elevations of the low water surface of the stream as correctly ascertained, 

 we can only consider the fall per mile, deduced from these computed distances, 

 as close approximations. 



The descent of the Mississippi, below the mouth of the Ohio, at low water, 

 may be confidently taken, as above, at an average of 2/o inches per mile ; and 

 that of the Ohio, from Evansville to its confluence with the Mississippi, at about 

 2to inches per mile. 



It has been suggested that the waters of the Gulf of Mexico stand much 

 higher than those of the Atlantic on the spheroidal surface of the earth ; for the 

 reason that the Gulf stream, setting always towards the north, must have a cer- 

 tain descent to account for its current. That current can only be due to a cer- 

 tain head at the source of the stream, since water in an open channel flows only 

 in virtue of the inclination of its surface. But the levels in the foregoing table, 

 which have been carried from the Hudson to the mouth of the Wabash, and 

 from the Gulf of Mexico to the mouth of the Ohio, agree so closely, that, while 

 we cannot dispute the theory, it is impossible, yet, to detect the fact. 



By observing the descent of the Alleghany from Franklin to Pittsburg, we 

 may conclude, that rivers, of which the fall does not exceed two feet per mile, 

 are navigable for steamboats, unless there be great irregularity in the distribu- 

 tion of that fall. In the event of such irregularity existing, rivers having an 

 average descent not exceeding two feet per mile, if well supplied with water, 

 must afford exceedingly good navigation between the rapids, which must be 

 very remote and easily overcome. 



We learn, also, from these tables, that a descent of nearly four feet per mile 

 is not incompatible with the existence of steamboat navigation, if the supply of 

 water be well maintained ; for a steamboat has ascended the Alleghany as far 

 as Olean Point, overcoming, in places, a slope of nearly five feet per mile. 



It is well known that the navigation of the Ohio, which, at certain seasons, is 

 scarcely surpassed on living streams, often fails for want of water of sufficient 

 depth to ffoat the boats that can be most advantageously used. It has been 

 proposed, at times, to remedy this defect by leading the water of Lake Erie into 

 the Ohio, and maintaining the navigation by supporting the depth in the channel 

 from that ample source. But it will be perceived by an inspection of the fore- 



