xliv INTRODUCTION. 
and newer pliocene periods; and to speak of the sum of the 
present observations under the term: “law,” may, perhaps, 
be deemed premature. But the generalizations first enun- 
ciated in my Report to the British Association in 1844, 
seemed to be sufficiently extensive and unexceptionable to 
render them of importance in a scientific consideration of 
the present distribution of the highest organized and last- 
created class of animals; and to show that, with extinct as 
with existing Mammalia, particular forms were assigned to 
particular provinces, and, what is still more interesting and 
suggestive, that the same forms were restricted to the same 
provinces at the pliocene periods, as they are at the present 
day.* 
In carrying back the retrospective comparison of recent 
and extinct Mammals to those of the eocene and oolitic 
strata, in relation to their local distribution, we obtain indi- 
cations of extensive changes in the relative position of sea 
and land during those epochs, in the degree of incongruity 
between the generic forms of the Mammalia which then 
existed in Europe, and any that actually exist on the great 
natural continent of which Europe now forms part. It 
would appear, indeed, from our present knowledge, that 
the further we penetrate into time for the recovery of 
extinct Mammalia, the further we must go into space to 
find their existing analogues. To match the eocene Pa- 
laotheres and Lophiodons, we must bring Tapirs from 
Sumatra or South America, and we must travel to the an- 
tipodes for Myrmecobians and Dasyures, the nearest living 
* Humboldt, in citing the Mylodon, Dinornis, and Diprotodon, briefly repeats 
my generalizations from those discoveries, and says: “ Es herrscht in Siidame- 
rika und in den Australindern eine grosse Achnlichkeit zwischen den dort 
lebenden und den untergegangenen Thieren.” “In South America and the 
Australian lands there prevails a great resemblance between the existing and 
the extinct animals.”—Aosnios, dyo. 1845, p. 303. 
