In 1847 he commenced the issue of his monumental three volume work, "Antiquités celtiques et antédiluviennes", a work in which he was the first to establish the existence of man in the Pleistocene or early Quaternary period. His views met with little approval, partly because he had previously propounded theories regarding the antiquity of man without facts to support them, partly because the figures in his book were badly executed and they included drawings of flints which showed no clear sign of workmanship.