224 A. Tylor on Changes of the Sea-Level effected by 
- wonld require five such periods to produce the quantity of detritus 
said to exist in the valley of the Mississippi; while it would re- 
quire fifty such periods to produce the requisite quantity of allu- 
Vitrm on the supposition that only one-tenth of the mud in ¢ransitu 
through the river was appropriated for the accumulation of its 
alluvial plains and delta. Under these circumstances it appears 
a legitimate conclusion, that the level of the sea cannot be con- 
sidered permanent for all practical purposes when it may be shown 
that it might be disturbed by the operation of present causes 
during the period occupied by the construction of a, single geo- 
logical formation. Elevations and subsidences of the land or sea- 
bottom would also effect important changes in the height of the 
sea-level, sometimes counteracting and at others adding to the 
effects produced by the continuous operation of rivers, &c. 11 
effects produced by these important causes would be an additional 
_ reason for not considering the sea-level permanent. * 
It is hardly necessary to add, that the continual waste of the 
earth’s surface by the carrying of materials into the ocean by 
rivers and breakers particularly attracted the attention of Hutton. 
He considered* that this was counteracted by elevatory move 
ments of the sea-bottom from time to time, but particularly men- 
tions that it was not necessary to suppose that the dry land was 
equally extensive at all periods. Since the fluctuation 10 the 
sea-level would be directly consequent upon the destruction of 
land arising from the operation of rain, the atmosphere, and rua: 
ning water on its surface, such changes would be in harmony 
with the spirit of the Huttonian theory. 
Part IIL. 
The average thickness of the deposit formed on the sea-bottom 
by the solid materials brought on to it from all sources has been 
estimated in the preceding part of the paper at 3 inches in 10,00 
years, producing an elevation of that amount in the sea-level 10 
the same period. Some portion of the oceanic area may be SUP 
posed to receive no part of this supply, while other localities 
nearer the coast-line obtain a great deal more than the averag® 
In the interval between these places, where the rate of deposit 1s 
extremely high, and those where it is extremely low, must lie an 
Pare detritus 
does not much differ from the average rate, which we have § ‘A 
more extensive near those parts of the ocean-bottom whl” e nip 
ceive no supplies of detritus whatever, but they must stretch "t 
to the coast-line in many places. For instance, if it 1s sup’ a 
* These remarks of Hutton are here introduced because he takes an entirely, 
ferent view of this subject to that promulgated by Sir Charles Lyell, who & 643) 
that there has been always an excess of subsidence. (See Principles, 1850, P 
