'but i assure you , dear lady , ' he said desperately , 'we are wizards . ' `` well , i was thinking of hanging around a bit . '' a metal arm carrying a tray with warm , sweet biscuits , and a large , steaming cup of hot cocoa extended itself . after all , there are hints about a higher civilization which had reached the bronze age , only to be thrown back by a natural catastrophe to another three thousand years or more of the stone age . '' 