170 DISTRIBUTION OF EXTINCT ANIMALS. [PART II. 
Distribution of Land Animals; and however imperfectly the task 
has been performed, the reader will at all events have been con- 
vinced that some such preliminary investigation is an essential 
and most important part of our work. So much of paleontology 
is at present tentative and conjectural, that in combining the 
information derived from numerous writers, many errors of detail 
must have been made. The main conclusions have, however, been 
drawn from as large a basis of facts as possible; and although 
fresh discoveries may show that our views as to the past history 
of 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 separate 
regions in the various geological epochs, or as to the centres 
from which some of the more important groups have been dis- 
persed. 
