w sound and good he would be. I doubt whether this
letter will be worth the reading.

LETTER 483. TO C. LYELL. Down [September 4th, 1849].

It was very good of you to write me so long a letter, which has
interested me much. I should have answered it sooner, but I have not
been very well for the few last days. Your letter has also flattered
me much in many points. I am very glad you have been thinking over the
relation of subsidence and the accumulation of deposits; it has to me
removed many great difficulties; please to observe that I have carefully
abstained from saying that sediment is not deposited during periods of
elevation, but only that it is not accumulated to sufficient thickness
to withstand subsequent beach action; on both coasts of S. America the
amount of sediment deposited, worn away, and redeposited, oftentimes
must have been enormous, but still there have been no wide formations
produced: just read my discussion (page 135 of my S. American book
(483/1. See Letter 556, note. The discussion referred to ("Geological
Observations on South America," 1846) deals with the causes of
the absence of recent conchiferous deposits on the coasts of South
America.)) again with this in your mind. I never thought of your
difficulty (i.e. in relation to this discussion) of where was the land
whence the three miles of S. Wales strata were derived! (483/2. In
his classical paper "On the Denudation of South Wales and the Adjacent
Counties of England" ("Mem. Geol. Survey," Volume I., page 297, 1846),
Ramsay estimates the thickness of certain Palaeozoic formations in South
Wales, and calculates the cubic contents of the strata in the area they
now occupy together with the amount removed by denudation; and he goes
on to say that it is evident that the quantity of matter employed to
form these strata was many times greater than the entire amount of solid
land they now represent above the waves. "To form, therefore, so great
a thickness, a mass of matter of nearly equal cubic contents must have
been worn by the waves and the outpourings of rivers from neighbouring
lands, of which perhaps no original trace now remains" (page 334.)) Do
you not think that it may be explained by a form of elevation which I
have always suspected to have been very common (and, indeed, had once
intended getting all facts together), viz. thus?--

(Figure 1. A line drawing of ocean bottom subsiding beside mountains and
continent rising.)

The freque