CHAPTER YI. 
THE EXTINCT MAMMALIA OF THE OLD WOULD, 
Although it may seem somewhat out of place to begin the 
systematic treatment of our subject with extinct rather than 
with living animals, it is necessary to do so in order that we 
may see the meaning and trace the causes of the existing dis- 
tribution of animal forms. It is true, that the animals found 
fossil in a country are very generally allied to those which still 
inhabit it ; hut this is by no means universally the case. If it 
were, the attempt to elucidate our subject by Palaeontology 
would be hopeless, since the past would show us the same 
puzzling diversities of faunas and floras that now exist. We 
And however very numerous exceptions to this rule, and it is 
these exceptions which tell us of the past migrations of whole 
groups of animals. We are thus enabled to determine what 
portion of the existing races of animals in a country are de- 
scendants of its ancient fauna, and which are comparatively 
modern immigrants ; and combining these movements of the 
forms of life with known or probable changes in the distribution 
of land and sea, we shall sometimes be able to trace approxi- 
mately the long series of changes which have resulted in the 
actual state of things. To gain this knowledge is our object in 
studying the “ Geographical Distribution of Animals,” and our 
plan of study must be determined, mainly, by the facilities it 
affords us for attaining this object. In discussing the countless 
details of distribution we shall meet with in our survey of the 
zoological regions, we shall often find it useful to refer to the 
evidence we possess of the range of the group in question in 
