The geographical distribution of animals, with a study of the relations ...

170 DISTRIBUTION OF EXTINCT ANIMALS. [part ii.Distribution of Land Animals ; and however imperfectly the taskhas been performed, the reader will at all events have been convincedthat some such preliminary investigation is an essentialand most important part of our work.So much of palaeontologyis at present tentative and conjectural, that in combining theinformation derived from numerous writers, many errors of detailmust have been made. The main conclusions have, however, beendrawn from as large a basis of facts as possible ;and althoughfresh discoveries may show thatour views as to the past historyof some of the less important genera or families are erroneous,they can hardly invalidate our results to any important degree,either as regards the intercommunications between separateregions in the various geological epochs, or as to the centresfrom which some of the more important groups have been dispersed.