My dear Mr. Agassiz.

I must write a line or two to thank you much for having written to me so long a letter on coral reefs—at a time when you must have been so busy.—² Is it not difficult to avoid believing that the wonderful elevation in the West Indies must have been accompanied by much subsidence, notwithstanding the state of Florida? When reflecting in old days on the configuration of our continents. the position of mountain chains, & especially on the long continued supply of sediment over the same areas; I used to think as probably have many other persons) that areas of elevation, and of subsidence must as a general rule be separated by a single great line of fissure, or rather of several closely adjoining lines of fissure.—³ I mention this because when looking within more recent times at charts with the depths of the sea marked by different tints, there seems to be some connection between the profound depths of the ocean, and the trends of the nearest though distant continents; and I have often wished that some one like yourself, to whom the subject was familiar would speculate on it.—

Believe me, Yours very sincerely. | Ch. Darwin.

P.S. I do hope that you will reurge your views about the reappearance of old characters, for, as far as I can judge, the most important views are often neglected unless they are urged & reurged—⁴

I am greatly indebted to you for sending me very many most valuable works, published at your Institution.⁵