216 A, Tylor on Changes of the Sea-Level. 
it cannot be employed for determining the quantity of the latter 
when associated in the water with a sulphid this case the 
stream of carbonic acid would carry with it the hydrosulphuric 
acid due to its reaction with the sulphids, as well as that existing 
ready formed in the liguid. For such a water, hydrogen gas u 
as above explained, is the proper displacing agent. 

Art. XXVII.—On Changes of the Sea-Level effected by existing 
Physical Causes during stated periods of time; by ALFRED 
Trtor, F.G.S. 
* 
(Concluded from page 32.) 
Part IL. 
Avuustons have already been made to the difficulty of proving 
whether or not the sea-level had been gradually elevated, be- 
cause the rise of the waters would conceal the evidence of theit 
former height except just at the mouths of rivers, where deposits 
of fiuviatile alluvium might raise the land from time to time 
keep it ahove the waves. The recent strata formed at a few 
-The 
sea-bottom is marked from the soundings on the Admiralty Chath 
and the depth of the Mississippi and its fuviatile deposit are ! 
serted from statistics collected by Sir C. Lyell.t 
: : the 
.* For a most valuable detailed description of the physical geography, &¢. oe 
miacg te and Ohio valley, see Mr, o. Ellet’s paper, Hentilacoian Contribution 
vol. ii, 1851, 
t See note, page 26, 
