Asks about CL’s new book [Travels in North America (1845)].

Discusses views of A. D. d’Orbigny on elevation.

Mentions reading W. H. Prescott [History of the conquest of Mexico (1843)].

Has at last received first letter CGE wrote.

More specimens being sent.

Sends his sketch of paper ["Fine dust in the Atlantic Ocean" (1846), Collected papers 1: 199–203].

D’Orbigny considers Pampas clay deposit result of debacle. CD cannot doubt it is slow, estuary deposit. Would be grateful for information on this point.

Acknowledges note and parcel for Ehrenberg.

Considers why different areas have different numbers of species. Gives an example opposing JDH’s view that paucity of species results from vicissitudes of climate. CD has concluded that species are most numerous in areas that have most often been divided, isolated from, and then reunited with, other areas. Cannot give detailed reasons but believes that "isolation is the chief concomitant or cause of the appearance of new forms".

Referring to a correspondent who had written about Pelargonium plants whose leaves had become regularly edged with white, CD reports that nearly all the young leaves of box-trees he had planted have become symmetrically tipped with white. Though these facts seem trivial, CD believes the first appearance of any peculiarity which tends to become hereditary deserves being recorded.

Asks whether salt and carbonate of lime (in the form of seashells) would act upon each other if slightly moistened and left in great quantities together. The question occurs from CD’s having found in Peru a great bed of recent shells that were mixed with salt, decayed and corroded "in a singular manner". Mentions, as relevant to the value of seashells as manure, that they are dissolved more rapidly by water than any other form of carbonate of lime.