Berry — Present Tendencies in Paleontology. 5 



more important boundaries. Where a well-marked time- 

 interval intervenes between two normal marine units 

 exposed to our investigation, it is easy sailing, but when 

 the hiatus is small or is partially bridged by marine 

 formations elsewhere, or by preserved continental sedi- 

 ments — disputation is endless. I need only cite in sup- 

 port of this contention the Hercynian, Rhaetic, "Wealden 

 and Laramie questions. When terrestrial sediments and 

 life replace marine sediments and life in a single section 

 or vice versa we insist that the particular marine fauna 

 vanished or appeared with the particular retreat or 

 advance of the sea in that region and that the terrestrial 

 fauna and flora appeared or vanished with the deposits 

 in which it is found. That the terrestrial and marine 

 organisms were contemporaneous over a much longer 

 interval than is represented by the particular associated 

 deposits is apparently never considered. This might be 

 illustrated by a discussion of the age of some of our Cre- 

 taceous formations, but I pass on to the broader question, 

 often lost to view, that our systematic units in so far as 

 their contained floras and faunas are concerned are 

 purely subjective academic pigeon-holes and if we had 

 the whole record we probably could not differentiate 

 Silurian from Devonian, Jurassic from Cretaceous or 

 Oligocene from Miocene. We have hoped for much from 

 the so-called method of diastrophism, and it has 

 undoubtedly immeasurably widened our stratigraphic 

 horizon and rationalized many outstanding problems. 

 As an absolute criterion for the determination of larger 

 units or as affording the basis for the rhythmic time- 

 table, it was foreordained to failure. I can see no more 

 reason for assuming that two successive cycles of sedi- 

 mentation correspond in relative duration, than there 

 would be for assuming that because a man, a turtle and 

 an elephant are born, live and die, that all endure for the 

 same number of years. Any succession of changes is 

 in a sense rhythmic, but the elaboration depends on the 

 location of a particular section with respect to the direc- 

 tion and distance of the basin from which the trangres- 

 sion emanated. We would make a sorry mess of it did 

 the segregation of Permian, Triassic or Jurassic rocks 

 depend on their visible development in North America. 

 The mid-Tertiary section in the northern Paris basin 

 represents nearly continuous sedimentation while farther 



