Origin of siliceous minerals sent by JH. Planning tenth edition of Principles of Geology. Convinced that changes in position of land and sea were principal causes of climate changes. Questions [James] Croll's theory of astronomical influences on climate, based on data from U. J. J. Le Verrier. Compares earth-pillars in Rhone valley with those in Tyrol. Wants tenth edition to include woodcut of JH's [1821?] drawings of earth-pillars.