554 Scientific Intelligence. 



rather than by shift! ngs of the seas. The fifty-seven maps were 

 planned to bring out this diastrophic basis for the geologic 

 periods, but beyond these eartb movements of the second order, 

 which separate the periods, are progressively smaller ones of the 

 third and higher orders which the maps and the curves con- 

 structed from them cannot show. For these the maps are still 

 too synthetic. 



A study of the work gives a very different impression as to the 

 character of North American paleogeography from that conveyed 

 by the older maps which figure in many text-books. The latter 

 show North America almost submerged at the beginning of the 

 Paleozoic and gradually emerging during the progress of that 

 long eon. The recent maps of Chamberlin and Salisbury, and 

 also those. of Willis and others, show quite a wide departure from 

 this older conception, but Schuchert's bring out one totally dif- 

 ferent. In the latter the amount of North America covered by 

 sea during eleven transgressions and ten emergences up to the 

 end of the Carboniferous averages 22 per cent, but the transgres- 

 sions being regarded as the longer phases, their average of 29 

 per cent represents the more permanent amount of water area. 

 Furthermore the maps do not show a gradual emergence and 

 growth of the continent such as have been formerly postulated, 

 but on the contrary far-reaching oscillations of the sea. This is 

 the dominating fact, but it is still true that after the greatest 

 transgression of the middle Ordovician each later inundation 

 covers somewhat less area. There is thus expressed graphically 

 and powerfully what has in recent years come to be believed by 

 many geologists, that wide oscillations of continental seas, pro- 

 ducing alternate intermingling and isolation of their faunas, 

 rather than a gradual retreat of the seas, was the controlling 

 principle of Paleozoic time. The maps in connection with the 

 discussions of the text give also a conception of the topographic 

 relief of the continent during this greater part of the fossil-bear- 

 ing earth record. The thin and patchy sediments representing 

 many epochs and the wide prevalence of limestone, the numerous 

 disconformities, only recognizable by finding hiatuses in the fos- 

 sil record, indicate the reign of extremely shallow seas lying on 

 lands which barely rose above their level. Except for the systems 

 of axes on the two sides of the continent which were elevated 

 from time to time and shed great quantities of waste into the 

 neighboring troughs, the continent was awash. Across now one 

 and now another part of this continental interior the ocean rolled 

 on and off in waves whose periods were measured by more than 

 a million of years. 



A review of so important a paper as this should not, however, 

 contain a mere summation of contents but also to some extent an 

 examination of the principles upon which it is constructed. Pro- 

 fessor Schuchert argues that unlike but synchronous faunas of 

 otherwise similar environment could not in the Paleozoic be 

 explained by differences in temperature of ocean waters or by sea 



