Sixteen copy letters and extracts of letters from Lyell to Moore and Croll. Four are summarised as August 1866 'On Climate', 'What small quantity of snow falls at North Pole - attraction of antipodal ice cap', 'On Croll's speculation as to thickness of ice at South pole', and 2 March 1866 'Heath suggestion of glacial [?] and his astronomical paper', and on 7 March 1866 'How does Adhémar melt the ice at one pole?'.