Mat 7, 1909] 



SCIENCE 



749 



America and Eurasia. In discussion Van Hise 

 pointed out the similarities between the two sets 

 of conclusions. 



The correlation of the major part of the Paleo- 

 zoic was discussed by Messrs. Walcott, Grabau 

 and Weller, whose papers comprised the period 

 from Cambrian to Mississippian, inclusive. Wal- 

 cott followed conservatively the lines of classi- 

 fication laid down in his earlier papers on the 

 Cambrian of North America. He felt obliged by 

 the state of investigations to confine his discus- 

 sion largely to evidence afforded by the brachio- 

 pods and indicated that more elaborate conclu- 

 «ions might be suggested by a similar thorough 

 study of the trilobites and other elements of the 

 faunas. Grabau discussed the faunas and sedi- 

 ments of Ordovician, Silurian and early Devonian 

 times, together with certain phases of the paleo- 

 geography and climatic conditions, especially of 

 New York and Michigan. Weller stated that 

 during Middle and Upper Devonian time the 

 faunas of North America occupied three prov- 

 inces, the eastern continental, interior continental 

 and the western continental. The provincial con- 

 ditions continued into early Mississippian time, 

 but gave place to more cosmopolitan conditions 

 through the development of the great Mississip- 

 pian province, with sub-provinces east of the 

 •CineiEmati arch and also in the western part of 

 .the continent. 



The late Paleozoic and early Mesozoic were 

 ■discussed by Messrs. Girty, David White and 

 Williston, with reference, respectively, to the in- 

 vertebrate faunas, the floras and the vertebrates. 

 Girty considered chiefly the relations of the 

 Pennsylvanian and possible Permian faunas of 

 North America, and their correlation with the 

 Permian of Russia. White brought out the world- 

 wide distribution of certain late Paleozoic floras 

 and touched upon the paleogeographic relations 

 •essential to their distribution. 



Williston was followed by Osbom, who dis- 

 cussed the Cenozoic vertebrates, and in the dis- 

 •oussion of their two papers the value of verte- 

 brate paleontology in its bearing upon former 

 land connections was distinctly apparent. 



In discussing the succession and distribution of 

 "the later Mesozoic invertebrates, Stanton con- 

 sidered late Jurassic, Lower Cretaceous and 

 Upper Cretaceous faunas in their bearing upon 

 the geography of those periods. A problem of 

 peculiar difficulty is presented by the marked 

 "distinction which exists between the Lower Cre- 

 taceous fauna of the gulf region and that of the 



Pacific coast, in spite of the fact that in Mexico 

 a Pacific fauna invades the western margin of the 

 province that was usually occupied by the gulf 

 fauna. In order to explain these relations it 

 appears to be necessary to recognize the probable 

 existence of a southern extension of the land area 

 of Arizona and its partial submergence first 

 from the east and then from the west. 



In discussing the conditions governing the dis- 

 tribution and evolution of Tertiary faunas, Dall 

 emphasized the importance of temperature of 

 marine waters and showed that in so far at least 

 as Tertiary and existing faunas are concerned, it 

 formed the dominant condition limitiog the 

 migration or continuance of the fauna. Follow- 

 ing Dall in the discussion of Tertiary faunas, 

 Arnold gave a detailed analysis of the Tertiary 

 of the Pacific coast, and exhibited maps showing 

 the geographic conditions at various stages from 

 Eocene to Pliocene. 



Closing the consideration of the historic suc- 

 cession, Knowlton discussed Mesozoic and Ter- 

 tiary floras, Salisbury brought out those phases 

 of physical geography of the Pleistocene which 

 had special relations to conditions bearing on 

 correlation, and MacDougal presented a consid- 

 eration of the origination of self-creating matter 

 and the influence of aridity upon its evolutionary 

 development. 



The symposium was closed by Chamberlin, who 

 discussed diastrophism as the ultimate basis of 

 correlation. The speaker emphasized the view 

 that diastrophism is the basal phenomenon ac- 

 cording to which other phenomena that afford 

 criteria for correlation are modified and devel- 

 oped. Taking a broad view of the whole subject, 

 he held that the periodicity of diastrophie move- 

 ments affords the criteria for determining the 

 major divisions, but he recognized also that all 

 the related lines of evidence are required to work 

 out the minutise of the problems of geologic cor- 

 relation. 



In connection with the discussions paleogeo- 

 graphic maps of North America at fifteen differ- 

 ent periods were exhibited. They represented 

 studies by Willis in association with a number of 

 colleagues in regard to the geologic provinces of 

 North America. 



The arrangements for the sympositmi on corre- 

 lation included one unusual feature, inasmuch as 

 a definite time schedule was prepared and pub- 

 lished in the program, and this schedule was 

 strictly adhered to during three days' proceed- 

 ings. In general, about three quarters of am 



