El autor encuentra temerarias todas aquellas opiniones que no coinciden en punto y hora con las suyas propias.       544   Although each formation may mark a very long lapse of years, each probably is short compared with the period requisite to change one species into another. I am aware that two palaeontologists, whose opinions are worthy of much deference, namely Bronn and Woodward, have concluded that the average duration of each formation is twice or thrice as…