Charles Darwin's geologist's field guide

From observations carried out on his 'Beagle' voyage, Charles Darwin made a number of important contributions to geological science. He showed himself to be a meticulous observer and an imaginative field worker. His methods are probably best summarized in a contribution on field geology that he made to the Admiralty Manual of Scientific Enquiry, published in 1849. That paper contains some important clues for the historian of early nineteenth-century geology.