Small insects swarm in all parts of tropics, though accompanied generally with large ones.
Thirdly, he appears influenced by the absence of newer deposits on the old area, blinded by the supposed necessity of sediment accumulating somewhere near (as no doubt is true) and being PRESERVED--an example, as I think, of the common error which I wrote to you about. The preservation of sedimentary deposits being, as I do not doubt, the exception when they are accumulated during periods of elevation or of stationary level, and therefore the preservation of newer deposits would not be probable, according to your view that Ramsay's great Palaeozoic masses were denuded, whilst slowly rising. Do pray look at end of Chapter II., at what little I have said on this subject in my S. American volume. (482/5. The second chapter of the "Geological Observations" concludes with a Summary on the Recent Elevations of the West Coast of South America, (page 53).)
I do not think you can safely argue that the whole surface was probably denuded at same time to the level of the lateral patches of Magnesian conglomerate.
The latter part of the paper strikes me as good, but obvious.
I shall send him my S. American volume for it is curious on how many similar points we enter, and I modestly hope it may be a half-oz. weight towards his conversion to better views. If he would but reject his great sudden elevations, how 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 frequency of a DEEP ocean close to a rising continent bordered with mountains, seems to indicate these opposite movements of rising and sinking CLOSE TOGETHER; this would easily explain the S.