'as if in ceaseless activity' The word 'ceaseless' means

'Ceaseless' comes from 'cease' (to stop) + '-less' (without), meaning 'without stopping' or 'continuous'. The passage describes thoughts as appearing and disappearing like clouds or waves — uninterrupted, ongoing activity. 'Continuous' best captures this meaning of uninterrupted, ongoing action. 'Permanent' implies lasting forever (different nuance), 'temporary' is the opposite, and 'flawless' means without defects (unrelated).