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.