GEOLOGICAL HISTORY OF THE PRIMATES 599 



short, and we must therefore be cautious in accepting stories 

 of stupendous geographical changes within that era. In 

 particular, the theory of a great trans-Atlantic connection 

 between Africa and South America, a connection persisting 

 till Middle Cainozoic times,* creates many more difficulties 

 than it solves. This theory has been supported by many 

 naturalists, including Berryman Scott. But whilst the hypo- 

 thesis helps us to account for the distribution of a few small 

 groups of mammals, it leaves the utter dissimilarity of the 

 respective mammifaunae of Africa and South America during 

 Eocene, Oligocene, and Miocene times completely unexplained. 

 It is, therefore, impossible to indicate all the routes followed by 

 the quadrupeds in the original dispersal. Nor is this surprising, 

 for the events in question took place in that mysterious time 

 represented in stratigraphy by the top of the Cretaceous and 

 the base of the Paleocene, and by the gap which so often exists 

 between them. We are much in the dark about this epoch. 

 What we do know is that the northern continents, Africa, and 

 South America all possessed stocks of placental mammals in 

 early Cainozoic times. 



It is necessary, in order to appreciate the character of the 

 problems surrounding the fossil Primates, to enter into certain 

 further details of historical zoogeography. As the reader is 

 aware, we divide the Cainozoic Era into the Paleocene, Eocene, 

 Oligocene, Miocene, Pliocene, Pleistocene, and Holocene (Recent) 

 Periods. It is useful to recall what these periods are. They 

 are, of course, pieces of time corresponding to certain stratified 

 rocks which happen to have been preserved for our edification. 

 These pieces of time are incomplete fragments of Cainozoic time. 

 They are, moreover, a European and North American series. If 

 the pioneer work in geology had been done in South America, we 

 should not have had the same series. Further, if we knew the com- 

 plete story of the Cainozoic we should sub-divide it on a different 

 principle : we should divide it, as we divide human history, by 

 the outstanding events. Now, we are not altogether in the dark 

 about the outstanding events of the Cainozoic ; through and 

 between the stratigraphical periods we can perceive other 

 periods, which are marked by these outstanding events. We 

 can see a partial but important discrepancy between the results 

 of these two methods of dividing the present geological era. It 

 is not a complete discrepancy, because the stratigraphical 

 divisions are, of course, founded on palseontological data ; 

 but the partial discrepancy is important for our present purpose. 



* The distribution of various groups of terrestrial invertebrates is said 

 to afiord evidence of such a trans-Atlantic connection in Mesozoic times. 

 But that is another question, which it is not the object of the present article 

 to discuss. 



