556 Scientific Intelligence. 



aided to some extent by marine planation, rather than that uplift 

 of the land should take place until it was exactly flush with the 

 surface of the sea. Schuchert's diastrophic curves are therefore 

 presumably too limited in width of oscillations and too smooth. 

 The latter point is illustrated by the Pleistocene, which is shown 

 on his curve as a straight line representing gradual emergence of 

 the continent to its present state, whereas it is known from the 

 drowned river valleys that geologically rapid and profound oscil- 

 lations have occurred and the continent now stands notably lower 

 than in that portion of the Pliocene when the mature valleys now 

 submerged were excavated. 



On the other hand, the study of faunas indicates that no great 

 oscillations have been missed and by adopting the most conser- 

 vative method of mapping Schuchert finds the marked oscilla- 

 tions which give him the basis for the new time scale. The 

 result proves the wisdom of caution in extending the limits of 

 the seas. But while the permanency of these maps and their 

 great value as a basis for future work is fully recognized, exten- 

 sions of the seas will probably be made in many cases by using 

 symbols such as Chamberlin and Salisbury and Willis have 

 employed to indicate probable but unprovable extensions beyond 

 the limits set by Schuchert. 



Passing next to that part of the paper which deals with the 

 causes rather than the results of paleogeographic change, the 

 great debt owing to Suess is made apparent. The chief cause of 

 the world-wide inundations is ascribed to the erosion of the lands 

 and the filling in of the seas, so that an erosion cycle is also an 

 inundation cycle. The emergences are ascribed to crustal move- 

 ments which increase the relief of the earth, chiefly by increasing 

 the volume of the ocean basins. The broad movements of the 

 strand line are therefore largely due, both negative and positive 

 movements, to changes of sea level, more than to movements of 

 the land, but it is especially in positive movements of the strand- 

 line that this is so. The problem, however, is by no means a 

 simple one and the author classifies continental seas according to 

 the dominant feature of their existence. The classification terms 

 are not mutually exclusive, since he regards nearly all as aggrad- 

 ing seas. During the period of advance they will be transgress- 

 ing seas and some of them will be synclinal seas. 



To this valuable part of the paper exception may be taken, 

 however, on two points. First, the author frequently ascribes 

 vertical warps, even in the continental interiors, to " thrusts from 

 the oceans," by which is meant of course " the oceanic crustal 

 segments." But it will be seen that for the collapse of geosyn- 

 clmes situated within continental platforms and often far removed 

 from the ocean basins, the immediate cause is a thrust between 

 two continental elements while the ultimate cause is held to be 

 the contraction of the earth's interior. Furthermore, horizontal 

 thrust in the crust has at most only a remote connection with 

 many vertical movements. " Thrusts from the oceanic segments " 

 is therefore an expression to be cautiously used, but as the 



