Cost books for mines in Cornwall, which also contain some draft and copy correspondence and some accounts of Richard Trevithick. Volumes one and two chiefly contain copy correspondence, mostly of Trevithick, especially with John Upreth Rastrick and with Hazledine, Rastrick & Co., although volume one is prefaced by 'Eastern Stray Park Costs' 1790-2, and volume two by Wheal Treasury costs 1795-7. Volume two concludes with some entries regarding Trevithick in South America. Volumes three and four chiefly contain accounts for mines from 1765 onwards and with numerous individuals c 1812-13.