October I, 1920] 



SCIENCE 



317 



longest studied and is best known, namely Eu- 

 rope and North America, show the greatest 

 amount of divergence even in formations as 

 recent and well preserved as those of the Ter- 

 tiary, and there are the most striking contrasts 

 in the geological history of Mediterranean as 

 compared with central and northern Europe. 

 The same situation exists upon all of the other 

 continents. 



Even supposing that changes in relative level 

 have been due to general causes such as the 

 periodic sinking of ocean basins and the fill- 

 ing of oceans by sediments,* which has not 

 been demonstrated and is directly opposed by 

 what we know of geological history, the re- 

 sults as reflected in those chapters of geolog- 

 ical history available for our study, would vary 

 with the initial attitude of the land in a par- 

 ticular area, its location with respect to the 

 position of the antecedent sea level, etc. A 

 striking illustration of this is furnished by a 

 comparison of the not very remote regions of 

 Belgium and the Paris basin, or even of the 

 center and periphery of the latter during the 

 Cretaceous and Tertiary. 



The question resolves itself into whether 

 geological classification in its major outlines 

 shall be local, that is, provincial and national- 

 istic, or whether it shall be understood and 

 capable of application in any country. I am 

 one of those reactionaries who believe that 

 classification is a means and not an end, and 

 that, however imperfect the scheme may be 

 as devised for the region first and longest 

 studied, namely Europe, the classic names 

 with the historic perspective that goes with 

 them, should be adhered to in this country. 



Classifications are all purely artificial, they 

 are the medium of exchange, and geological 

 time boundaries are no more physical facts 

 than are political boundaries, even though it 

 may be difficult to avoid thinking of them as 

 though they are entities. Probably the best 

 ultimate solution would be to have a universal 

 (international) time scale and a local sedi- 

 mentary scale as we now have for our forma- 



* A simple quantitative eomputation will show 

 how trifling would be the maximum change in sea 

 level from the latter. 



tional units. After all the best classifications, 

 whether of geological time, systems of rocks, 

 organisms or igneous rocks, are those most 

 easily understood and used, those in which 

 facts and relationships are not obscured or 

 wholly disguised by names. 



Time is continuous, boundaries are always 

 subjective, and the Permian, Triassic, Lower 

 Carboniferous or Lower Cretaceous are to me 

 as essential to clear thinking and the inter- 

 change of ideas among nations as are the 

 minutes, hours, days and weeks of current 

 chronology, however illogical these might seem 

 in sidereal astronomy. 



The problem of correlation would be im- 

 mensely simplified if diastrophism could be 

 demonstrated to be of universal application. 

 This is I believe the reason it has so appealed 

 to many, but like its prototype devised by 

 Werner it is altogether too simple to be true. 



It seems to me that the inost reliable basis 

 of correlation must remain paleontologic until 

 such time as it can be shown that changes of 

 relative elevations are due to changes of sea 

 level, and if this be true there is a disturbing 

 factor in attempting to settle the relative 

 merits of homotaxis versus synchroneity. I 

 have a feeling, however, that homotaxis, al- 

 though theoretically true, has been greatly 

 overestimated in its bearing upon our interpre- 

 tations of geological history where we do not 

 have continuous sedimentation to deal vrith. 



Paleontologic correlation, it should be need- 

 less to remark, rests ultimately upon the syn- 

 thesis of all classes of organic evidence, not 

 merely upon invertebrates, vertebrates or 

 plants. How little this truism is observed in 

 practise and to what an extent geological 

 thought is still permeated by Cuvier's cata- 

 clysmal philosophy can be appreciated by 

 reading any recent discussions of the boundary 

 between the Devonian and Carboniferous, the 

 Triassic and Jurassic, the Jurassic and Lower 

 Cretaceous, or the Upper Cretaceous and Ter- 

 tiary. Accepting the doctrine of evolution for 

 life and of uniformitarianism for earth his- 

 tory, the average stratigraphic paleontologist 

 seems determined to prove cataclysms and 

 special creation. 



