Page:Popular Science Monthly Volume 9.djvu/562

536 Neotropical region is not only distinguished as the headquarters of the Phyllostomidœ, but also by being altogether destitute of the flying-foxes and Rhinolophidœ.

Such being the relation of bats to space—their geographical distribution—what are their relations to time—their geological distribution?

I assume that my readers are acquainted with the fundamental facts and laws of geology, and know that the successive layers, of which the superficial crust of the earth is in very various degrees composed, are classifiable into three sets: 1. The Primary or Palæozoic rocks; 2. The Secondary or Mesozoic rocks (from the Trias to the Chalk inclusively); and, lastly, 3. The Tertiary or Cainozoic rocks, extending upward from the Chalk to the present day.



Remains of beasts more or less closely resembling some of those existing now in Australia are found low down in the secondary rocks, namely, in the Triassic and Oolitic formations. Generally speaking, however, beasts such as those which now exist are not found deeper than the Tertiary strata, and this is the case with bats.

The oldest fossil bat yet known is represented by a few teeth found in Eocene deposits in Suffolk. The oldest perfect fossil bat is the Vespertilio Parisiensis of the gypsum-bed of Montmartre, near Paris.

Some forms of existing beasts, however, which are now distinct enough, such as the ox and the pig, or the tapir and the horse, were