264 Mr. A. Tylor on Changes of the Sea-Level effected hy 



proof could be brought forward of a recent gradual upward 

 movement of the sea-level. This, however, would be difficult to 

 observe*, on account of the rise in the water concealing the evi- 

 dence of its former level, except just at the mouths of rivers, 

 where the deposits of fluviatile alluvium might raise the land 

 from time to time and keep it always above the rising waters. 



The deposits situated at a few such localities have been de- 

 scribed by the best observers, and I hope to show that in several 

 cases there are appearances which might be partly explained by 

 changes of the sea-level, but that a much greater number of cases 

 and more certain evidence would be needed before such an event 

 could be satisfactorily proved. I propose to make some remarks 

 upon this point, after having submitted the evidence which has 

 induced me to believe that the supply of detritus under present 

 physical conditions is sufficient to raise the ocean level 3 or 4 

 inches in 10,000 years, provided no subsidence or elevation 

 disturbed the result. 



To this subject I now proceed. Sir Charles LyelPs published 

 statements of the quantity of mud annually carried down by the 

 Mississippi and Ganges appear to have been made with so much 

 care, that they may be a better guide to the general rate of 

 removal of soil by rivers than information obtained from a greater 

 number of smaller rivers, which of course are more likely to be 

 influenced by local circumstances. Eleven hundred thousand 

 square miles of land are drained by the Mississippi f, which annu- 

 ally discharges a quantity of water equal in volume to 4 inches 

 of rain, or about one-tenth of the total rain-fall over this entire 

 surface, which forms one-fifth part of North America J. From 

 the mean of a great number of observations, the average quantity 

 of alluvium suspended in the water appears to be 1 part in 3000. 

 Consequently, as the water annually drawn off would cover an 

 area of eleven hundred thousand square miles to the depth of 4 

 inches, the quantity of mud removed in the water (as measured 

 at or near the mouth of the river) would cover the same exten- 

 sive surface to the depth of ^^\j^dth part of 4 inches, or to the 

 depth of ^^\j^dth part of a foot. Or, in other words, the Mis- 

 sissippi at its present rate would occupy 9000 years in carrying 

 away detritus before the mean surface-level of one-fifth part of 

 North America would be reduced 1 foot. 



The Ganges discharges into the Indian Ocean a supply of 



wasted exactly in proportion as new land shall appear ; or conversely, that 

 an equal proportion of new land should be produced as the old is made to 

 disappear." (Hutton's Theory of the Earth, 1795, vol. i. p. 196.) 

 ♦ See Darwin, Coral Reefs, &c., edit. 1851, p. 96. 

 t See art. Mississippi, Penny Cyclopaedia, vol. xxv. p. 277- 

 X The total rain-fall of the United States is 39 inches between 24i° and 

 45* N. lat. (Berghaua and Johnston.) 



