316 



SCIENCE 



[N. S. Vol. LII. No. 1344 



pretation involves considering the treak in 

 sedimentation at the bottom of the Manzano 

 group of that region, of which the Abo is the 

 lowest formation, as having occurred during 

 so-called Pennsylvanian time, and would place 

 the boundary between the Pennsylvanian and 

 the Permian at some undetermined horizon 

 within the Manzano group of conformable for- 

 mations, as Lee^ has pointed out. I would not 

 be in the least surprised if this last is not the 

 true interpretation of the facts. It is just what 

 would be expected by any one disposed to 

 doubt the validity of the so-called diastrophic 

 method of correlation, and, if I mistake not, 

 is exactly what occurs in the Appalachian re- 

 gion. 



The second paper to which I refer is one by 

 TwenhofeP who concludes that all of the Cre- 

 taceous below the Benton in Kansas should be 

 referred to the Comanchean, and that the 

 Cheyenne-Kiowa-Medicine sequence of south- 

 ern and the Mentor-Dakota sequence of cen- 

 tral Kansas are the equivalents of the Washita 

 division of the Texas Cretaceous, although it 

 is conceded that the Washita faunas and floras 

 are probably of Cenomanian age and there- 

 fore Upper Cretaceous according to European 

 chronology. 



Without discussing the merits of these con- 

 clusions in this place, I wish to call attention 

 to the more general question involved, which 

 is clearly recognized by Lee in connection with 

 the Manzano group, and which is discussed at 

 some length by Twenhofel in connection with 

 the Kansas Cretaceous, namely as to what 

 are the criteria of systematic boundaries. 



1 can see no fundamental objection to using 

 such terms as Comanchean as a convenient 

 group or descriptive term any more than in 

 using such terms as Mississippian or Penn- 

 sylvanian, disregarding even that Mississippian 

 in its original significance was Cambrian, but 

 to use Comanchean as the equivalent of the 

 European Lower Cretaceous, which it is not 

 in either its lower or upper limits, and thus 

 to bring about a situation where Lower Cre- 



2 Lee, W. T., Idem, pp. 323-326, May, 1920. 



3 Twenhofel, W. H., Idem, pp. 281-297, April, 

 1920. 



taceous in Europe, Asia, Africa, Australia, 

 and South America means Lower Cretaceous, 

 whereas Lower Cretaceous in the United States 

 means early Upper Cretaceous, appears to me 

 most reprehensible. 



American geological literature has been de- 

 luged, one might almost say diluted, with dias- 

 trophism during the last decade, and philoso- 

 phers, scientific as well as political, stand on 

 every street corner. Whether there is any 

 world wide periodicity in movements of the 

 strand line as Suess and Chamberlin contend, 

 or whether each region has its individual his- 

 tory as Willis contends, I do not know, al- 

 though what we know of geological history is 

 all in favor of the latter supposition. I should 

 imagine that sometimes one and sometimes the 

 other might be true, depending entirely on the 

 causes that affect the relative positions of the 

 land and sea in specific cases. 



I certainly can see no basis for the " law of 

 periodicity" that Willis writes about beyond 

 the partial fulfillment of ISTewberry's much 

 older conception of cycles of sedimentation, 

 which are no more comparable in chronologic 

 magnitude than are the life cycles of or- 

 ganisms. 



If American geology is to finally adopt dias- 

 trophism as the ultimate basis for the delimi- 

 tation of the more impoi'tant time boundaries, 

 and it is already clear that the geologists of 

 no other nation are likely to follow our lead, 

 we shall have to devise a different terminology 

 for each continent, or even for different parts 

 of the same continent. Eor example on our 

 Pacific coast there were Triassic floodings 

 that have been successfully correlated by 

 Smith on the basis of their ammonite faunas 

 with those of the Mediterranean region of the 

 old world. On our Atlantic coast there are no 

 traces of any corresponding events. Exactly 

 similar conditions prevailed in the two gen- 

 eral regions during the Jurassic. Lower Cre- 

 taceous marine sediments are confined to the 

 southern and western parts of North America, 

 and one might start at the bottom of the geo- 

 logical column and point out very many simi- 

 lar contrasts. 



The two continents whose geology has been 



