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.

Preparing fifth edition of Principles of Geology, using JH's facts about boiling seeds. Mathematical error in CL's climate theory. CL's first speech as president of Geological Society. Criticizes R.S.L. JH's volcanic theory was too complex; will incorporate it into later editions. Benefits to science of Charles Babbage's social parties. Latest publications in geology. P.S. Glad to learn that JH thinks origin of new species may occur through intermediate causes; Germans criticized this. CL chooses not to engage in controversies. Speculates on successive extinction of species. Notes on African hot springs.

Charles Lyell wrote letter to JH recently. Now encloses with it letters of introduction to persons in Rio and abstract of paper by Charles Babbage. [Henry] Brougham's attacks on Thomas Young.