Johnston, historian Nikolaus Pevsner and landscape historian Richard Muir all agree that an original gravel surface dressing was once present on top of the stone of the Wheeldale structure. Whereas Johnston and Pevsner believe that the gravel was washed away through weathering, Muir states that human agents were primarily responsible for its removal. Both agree that the stonework remaining does not represent the original road surface. Statements by the eighteenth-century antiquary Francis Drake and nineteenth-century topographer Samuel Lewis that the writers found it to be "paved with a flint pebble" may support this theory, although Hayes and Rutter cast doubt on the accuracy of Drake's reports. Codrington states that in 1817 the causeway consisted of a "strong pavement of stones ... above these another stratum of gravel ...", Hayes and Rutter state that "traces of a surface layer of gravel and small stones" remained visible in the 1960s, and professor of structural engineering John Knapton states that there remained some evidence of smaller surface-dressing pebbles as late as 1996.