2 74 ROLLIN D. SALISBURY 



last flora to its present latitude. The first five members of the succes- 

 sion seem to correspond with the half of a normal interglacial series. 

 If this interpretation is correct, this series of five floras would be nearly 

 doubled with the on-coming of another glacial epoch, and this doubled 

 series must have been repeated, substantially, several times in the 

 course of the long succession of glacial epochs. Fragments of inter- 

 glacial records have been found both in America and Europe. In a 

 few cases they are full enough to encourage the hope that when their 

 number is duly increased, they may be pieced together into consistent 

 wholes. It is too much to expect that they will ever be as complete 

 as the record of post-glacial life. 



It is not now apparent just how far biologic or paleontologic data 

 of the Pleistocene, except for their record of climatic changes, are 

 to be significant in correlation. Aside from the mammals, changes 

 of species have been insignificant. Even among mammals, it is not 

 clear that the dying-out of species in one locality was contemporaneous 

 with the disappearance of the same species in other localities. A 

 stratigraphic basis for this interpretation would be needed before it 

 could be accepted. So far as all other forms of life are concerned, 

 the paleontologic record of one interglacial epoch must have been 

 essentially identical with that of another, if the intervals were equally 

 long and mild. 



Perhaps more help in correlation may be looked for in another 

 direction. Intercontinental migrations, it would seem, must have 

 been virtually restricted to interglacial epochs. The times when 

 species first appeared in a given region may therefore prove to be 

 much more significant in correlation than the times when species 

 died out. 



Something perhaps may be hoped for in the careful study of the 

 records of oscillations of level, during the period; but it seems clear 

 that different parts of the same continent have suffered minor or even 

 considerable deformations, independently of others. If it were 

 established that opposite sides of an ocean basin were less independent 

 in this respect — a doctrine for which much might be said — the 

 movements on opposite sides of an ocean basin might be a hopeful 

 line of research; but it cannot, at the present time, be said to have led 

 to important conclusions. 



