My dear Mr Agassiz.

It was very good of you to write to me from Tortugas, as I always feel much interested in hearing what you are about, and in reading your many discoveries— It is a surprising fact that the peninsula of Florida should have remained at the same level for the immense period requisite for the accumulation of so vast a pile of debris—¹

You will have seen M^r Murrays news on the formation of Atolls & barrier reefs—² Before publishing my book, I thought long, over the same view, but only as far as ordinary marine organisms are concerned for at that time little was known of the multitude of minute oceanic organisms. I rejected this view as from the few dredgings made in the Beagle in the S. Temperate regions, I concluded that shells, the smaller corals &^c &^c decayed & were dissolved, when not protected by the deposition of sediment; & sediment could not accumulate in the open ocean. Certainly shells &^c were in several cases completely rotten and crumbled into mud between my fingers; but you will know well whether this is in any degree common.— I have expressly said that a Bank at the proper depth would give rise to an atoll, which could not be distinguished from one formed during subsidence; I can however hardly believe, in the former presence of as many banks (there having been no subsidence) as there are atolls in the great oceans, within a reasonable depth on which minute oceanic organisms could have accumulated to the thickness of many hundred feet.³ I think that it has been shown that the oscillations from great waves extend down to a considerable depth, and if so the oscillating water would tend to lift up. (according to an old doctrine propounded by Playfair) minute particles lying at the bottom, and allow them to be slowly drifted away from the submarine bank by the slightest current.⁴ Lastly I cannot understand M^r. Murray, who admits that small calcareous organisms are dissolved by the Carbonic acid in the water at great depths, & that coral reefs. &^c &^c are likewise dissolved near the surface but that this does not occur at intermediate depths, where he believes that the minute oceanic calcareous organisms accumulate until the bank reaches within the reef-building depth—⁵ But I suppose that I must have misunderstood him.— Pray—forgive me troubling you at such length, but it has occurred (to me?) that you might be disposed to give after your wide experience, your judgment. If I am wrong, the sooner I am knocked on the head and annihilated so much the better. It still seems to me a marvellous thing that there should not have been much & long continued subsidence in the beds of the great oceans.— I wish that some doubly rich millionaire would take it into his head to have borings made in some of the Pacific and Indian Atolls; and bring home cores for slicing from a depth of 500 or 600 feet.⁶

Believe me my dear M^r. Agassiz. | Yours very sincerely— | Charles Darwin.

P.S. I read with much interest your address before Am: Soc: Adv: of Sc:  However true your remarks on the genealogies of the several groups may be, I hope & believe that you have overestimated the difficulties to be encountered in the future.—⁷ A few days after reading your address, I interpreted to myself your remarks on one point (I hope in some degree correctly) in the following fashion.

This idea seems to me to throw a flood of light on the lines, sometimes used to represent affinities, which radiate in all directions, often to very distant sub-groups.— A difficulty which has haunted me for half a century— A strong case could be made out in favour of believing in such reversion or atroversion⁸ after immense intervals of time— I wish the idea had been put into my head in old days. for I shall never again write on difficult subjects as I have seen too many cases of old men becoming feeble in their minds, without being in the least conscious of it— If I have interpreted your ideas at all correctly I hope that you will reurge on any fitting occasion your view— I have mentioned it to a few persons, capable of judging and it seemed quite new to them.— I beg you to forgive the proverbial garrulity of old age.

C.D.