DISTRIBUTION OF MAMMALIA TN TIME, 617' 



Miocene rocks occur numerous small Rodents. In the Plio- 

 cene and Post-pliocene deposits the order is also well repre- 

 sented, the most remarkable form being the Great Beaver 

 {Trogontheritim), which appears to have survived into the his- 

 torical period. 



Order XL Cheiroptera. — The earliest-known indications of 

 Bats are in the Eocene period, but the order is of no geological 

 importance. 



Order XII. Insectivora. — The Insectivorous Mammals, like- 

 wise, commenced their existence, so far as is known, in the 

 Eocene period ; and they, also, are of no importance from a 

 geological point of view. 



Order XIII. Quadrumana. — The earliest-known remains of 

 Quadrumana occur in the Miocene period. Several genera 

 are known, but the most important are Pliopithecus and Dryo- 

 pithecus, both of which are European, and both of which belong 

 to the section of the Catarhine Monkeys which are at present 

 characteristic of the Old World. They appear to be most 

 nearly allied to the recent Gibbons. It is interesting to notice 

 that the American fossil Monkeys — from the later Tertiary 

 deposits of South America — belong to the division of the Quad- 

 rumana now peculiar to that continent — to the section, 

 namely, of the Platyrhine Monkeys. 



Geographical Succession of Organic Forms. 



A few words may be said here on a law which may be called 

 the " law of the geographical succession of organic forms," and 

 which is illustrated more completely by the Mammalia than by 

 any other extinct animals. An examination, namely, of the 

 facts of the geological distribution of Mammals leads to the 

 striking generalisation that " the present distribution of organic 

 forms dates back to a period anterior to the origin of existing 

 species'" (Lyell). In other words, though the extinct Mam- 

 mals of the later geological deposits of any given country differ 

 specifically from those now existing in the same country, they 

 are nevertheless referable to the same orders, and are in every 

 respect more closely allied to the present Mammalian fauna 

 than to that of any other country. A few examples will render 

 this perfectly clear. 



Australia at the present day is an altogether peculiar zoolo- 

 gical province, characterised by the abundance and variety of 

 Marsupials wliich inhabit it. In the Post-tertiary deposits of 

 Australia, however, we are presented with proofs that Marsu- 

 pials were just as characteristic of Australia during late geolo- 



