At the age of twenty-one De la Beche joined the Geological Society of London. He became an avid fossil collector and illustrator, collaborating with William Conybeare on an important paper on ichthyosaur and plesiosaur fossils from Lyne Regis and their anatomy. His paper was presented before the Society in 1821. He continued throughout his life to be one of its most active, useful and honoured members, serving as president of the Society from 1848 to 1849. He visited many major geological localities, not only in Britain, but also in France, Jamaica and Switzerland. In stayed in Jamaica in 1823–1824 and published his geological account of Jamaica in 1827. Returning to the south-west of England he began a detailed investigation of the rocks strata and mineral deposits of Cornwall and Devon. Contact with the mining community of that part of the country gave him the idea that the nation ought to compile a geological map of the United Kingdom, and collect and preserve specimens to illustrate, and aid in further developing, its mineral industries. The results of his studies of the Cornwall and Devon region are found in his 1839 book “Geology of Cornwall Devon and West Somerset”. Complete copies of the work are now scarce.