Having read John Burrow's book, JH proposes procedure for analyzing masses of data from [African] Expedition. Will volunteer to interpolate chronometer errors if TM will undertake computations.

Speculates on extinction of species by natural (not miraculous) causes intermediate to Creator. JH's theory of shifting crust over Earth's surface and its subsequent transfer of pressure. Seeks geological primum mobile for volcanoes based on continual deposition and melting of strata. 'All records of former worlds must ultimately perish.'

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.

Unable to send the Parramatta observations as the vessel is leaving too soon. Has just returned from a meeting to consider [William?] Ritchie's new optical glasses. George Dollond speaks well of them.