Berry — Present Tendencies in Paleontology. 9 



late there has been a tendency to deny altogether the 

 validity of the homo tactic viewpoint. 



The question is vital in a consideration of past evolu- 

 tion, distribution, climatic conditions and paleogeog- 

 raphy. It is also almost infinitely complex, and there are 

 various underlying conceptions such as the rate of spread 

 of different classes of organisms and the degree of cos- 

 mopolitanism reached by marine organisms during times 

 of land emergence and of terrestrial organisms during 

 times of submergence when the obverse records are 

 largely wanting, that have a very important bearing. If 

 the conditions, both geographic and topographic, which 

 are predicted for the various Appalachian troughs or 

 basins during Paleozoic time, are correctly interpreted, 

 as there seems to be no reason for doubting, we are intro- 

 duced to an environment which is special in the sense 

 that it is not duplicated at the present time anywhere on 

 the earth's surface so far as I can see. This being true 

 the generalizations derived from the study of the over- 

 laps and the rapid floodings of these Appalachian basins 

 must be applied with great caution to other sets of con- 

 ditions such as determined the broad seas of Jurassic, 

 Upper Cretaceous or Eogene times. 



If our present Coastal Plain margin were to take 

 another dip beneath the ocean, would it be possible for 

 the paleontologist of a million years hence to establish 

 the synchroneity of deposits formed at the same time 

 along our middle Atlantic and Gulf coasts or to differen- 

 tiate these chronologically from such late Pleistocene 

 shell marls as those at Wailes Bluff at the mouth of the 

 Potomac or Simmons Bluff in South Carolina? I think 

 it would be feasible, and am inclined to disagree with the 

 universality of the statement (Ulrich) that for strati- 

 graphic purposes the coarseness of the distinguishable 

 chronologic units obviates the necessity of attempting to 

 deal with the theoretically true time involved in dispersal. 

 This may be perfectly true, however, of some of the Paleo- 

 zoic transgressions over the base-levelled Appalachian 

 troughs and also when dealing with marginal invasions 

 around the borders of a single oceanic basin where the 

 faunas have had time to become generally distributed. 



Our conclusions usually do not rest upon irrefutable 

 logic, however, and it is most important to determine by 

 closer analysis the interlacing waves and ripples of dis- 



