Galapagos land birds and reptiles.

No two naturalists agree on any fundamental idea [of species]. "Everything is arbitrary."

Has been with Richard Owen going over the S. American fossils.

Has worked out the non-relation between animals’ bulk and luxuriance of vegetation.

The horse once common on the Pampas. The mystery of the extinction of these animals.

Responds to Lyell’s query [missing] about northern and southern limits of coral islands of the Pacific. Warns that coral islands are much more thinly distributed than people realise and cites examples. Comments on views of Matthew Flinders. Reading work of É[lie] de B[eaumont]. Notes difficulty of setting an east-west boundary to coral islands.

Comments on receiving copy of Lyell’s Elements [of geology]. Much is new to CD, and he is copying out notes and references.

Criticises geological work of John Phillips.

Describes expedition to Glen Roy, about which he is writing a paper ["Parallel roads of Glen Roy" (1839), Collected papers 1: 87–137].

Enjoys the Athenaeum Club.

Criticises entomological work of F. W. Hope.

Asks Lyell to obtain for him a copy of barometric readings made at Leith.

Asks him to ascertain altitude of several Scottish lochs.

Comments on FitzRoy’s character.

Comments on an article in Edinburgh Review [by David Brewster, 67 (1838): 271–308] on Comte’s Philosophie positive.

Discusses falsity of Élie de Beaumont’s views of contemporaneous parallel lines of elevation and subsidence.

Owen’s views of relationship of reptiles to birds.

On "question of species" CD has filled notebook after notebook with facts, "which begin to group themselves clearly under sub-laws".

Announces his engagement to Emma Wedgwood.

Discusses his Glen Roy paper [(1839), Collected papers 1: 87–137], which he is sending to CL.

Remarks on Charles MacLaren’s treatment of alluvium. Comments on alluvial action in Lochaber.