No summary available.

Thanks CL for the gift of a new edition of CL's Principles of Geology. JH comments on a number of issues, in a very long letter, including the replacement of extinct species by other species, CL's solution of the problem of the variation of climate, and the evolution of language. JH speculates at length on the isothermal activity under the earth's crust that may result in volcanoes or the formation of new land masses, and describes a considerable number of geological examples that JH sees as supporting CL's ideas.

Ideas expressed by JH in his previous letter to CL (see JH's 1836-2-20) about secular variations of isothermal surfaces of the interior of the earth were similar to ideas expressed by Charles Babbage in a paper to the Geological Society. This was drawn to JH's attention by CL and by R. I. Murchison. JH argues that he did not know of Charles Babbage's paper, and goes on to point out how JH's ideas differ. Concludes with mention of having re-discovered the sixth satellite of Saturn, not seen since its discovery by JH's father, William.

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.

Impressed by CD’s theory [of earthworm action].

Sends four samples of dust blown on board his ship from the coast of Africa, nearly 400 miles away, during four days in March 1838. Gives careful descriptions and relates the tests he made of it [see Collected papers 1: 200].

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.