22 A. Tylor on Changes of the Sea-Level effected by 
water to cause an elevation of the ocean-level to the extent of at 
least 3 inches in 10,000 years. 
In the Second Part an endeavor is made to compute the num- 
ber of such periods of 10,000 years that must have elapsed dur- 
ing the accumulation of the immense mass of recent freshwater 
strata said to exist in the valley of the Mississippi. 
The calculation as to the latter is made from the data collected 
by observers in America, of the extent of the deposit in question ; 
and it is here supposed, first, that in former periods the same 
quantity of mud as at present has been annually carried into the 
Gulf of Mexico; and secondly, that the amount of sediment de- 
posited on the delta and plains of the Mississippi does not exceed 
one-tenth part of the solid material which has been carried out 
(suspended in the water of the river) into distant parts of the 
Gulf of Mexico, or into the Atlantic Ocean itself. 
From recent accounts by Mr. C. Ellet, of the United States, it 
appears that a column of fresh water, 14 mile wide and about 7 
feet deep, is constantly entering the Gulf of Mexico at a speed of 
2 to 24 miles per hour, and floats on the surface of a stratum of 
salt water, to which it partially communicates its own velocity. 
And below this a stratnm of sea-water is found to be flowing in 
an opposite direction to that of the two strata of fresh and salt 
water above it. See figs. 1 and 2. 
From the data submitted, it would appear that the accumula- 
tion of the alluvial deposit of the Mississippi must have occupied 
a great number of periods, during each of which an elevation of 
the sea-level of 3 inches may have occurred. 
erable change in its height, even during the construction of a re- 
cent deposit like that in the valley of the Mississippi, which ma 
be called small and local compared with those older formations 
familiar to geological observers. 
the subsidence arid elevation of the crust of the earth 
would be accompanied by alterations of the area of the sea-bed ; 
and the frequency of such movements would therefore furnish 
additional reasons for not considering the sea-level permanent for 
the lengthened periods requisite for the accumulation of sedi- 
mentary deposits of any magnitude. : 
In the Third Part of this paper an attempt is made to direct 
attention to the difficulty of finding any test by which to distin- 
guish strata gradually accumulated during a long-continued up- 
ward movement of the sea-level, from those strata formed on 4 
sea-bottom slowly subsiding while the ocean-level was station- 
ary. In either case no change of depth of water may have oc- 
curred of sufficient importance to cause the removal of the Mol- 
