196 GEOLOGICAL SURVEY 
influence of the salt water, and the Cedars are gradually disappearing before it, and in a few years 
there will be scarcely one left, unless the salt water may again become sufficiently diluted by the 
retardation of the fresh water of the river. 
The ground upon which these cedars stand is mud, too soft to support the weight of a man; so 
that a pole may be thrust down into it ten or twelve feet. And it is a fact worthy of notice, that 
this is the case wherever Cypress stumps are submerged—at least so far as I have had opportunity 
of observing. They are always buried in soft mud. 
These flats have high, firm land every where adjoining them, which have trees growing to their 
very edge, and we have no reason to assume that it was ever different. I examined the points of 
contact of the two, with great care, to ascertain whether or not there may be stumps in the firm 
land, below the level of tide: if so, the proofs of subsidence presented by these Cypress stumps, 
would be indisputable; but I did not find a single one. Now as I cannot conceive of a subsidence 
confined to a swamp, for such these marshes once were, and following all its sinuosities, without 
affecting the firm land adjoining, Iam obliged to seek some other explanation of these submerged 
stumps. 
The Cypress swamps of South Carolina, and I believe elsewhere, are composed, for the most 
part, of a vast accumulation of vegetable matter,* often covered with Sphagnum, Ferns, and a thick 
undergrowth of shrubs, the whole preventing evaporation and decomposition, and retaining mois- 
ture like a sponge. 
Now the effect of the encroachment of salt water upon such a swamp as this would, in the first 
place, be to kill the undergrowth, and expose the soil to the sun and light; decomposition of the 
vegetable matter would proceed rapidly; the trees would decay and fall, breaking off the “air-line.” 
The organic ingredients of the mass of vegetable matter would pass off into the atmosphere, and 
the rest, saturated with water, would be converted into mud. Can any one suppose that a deposit, 
thirty or forty feet in thickness, would not sink, under such a process, sufficiently to account for the 
position of these stumps? 
Should the overflow of water continue, a sedimentary deposit would take place above the stumps, 
and should the salt water be again shut out, another growth would succeed the Cypress, such as 
the Cedars of the Cedar islands; and these again may be killed, as is the case on those islands, by 
a second encroachment. How such alternations take place will next be shown. 
Fig. 33 is a reduced map of Murphy’s Island, at the mouth of 8. Santee, taken from an accurate 
survey, made in 1850. 4 
* See a paper on the Cypress Timber of the Mississippi, by Dr. Dickeson and A. Brown, Sill. Jour. Jan. 1848, 
