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.