298 THE JOURNAL OF GEOLOGY. 



parts of the country should be published without waiting longer 



for a perfect method of coloring to be devised. J. P. I. 



*. * 

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Do oscillations of the crust progress by waves ? Or are 

 they limited to non-progressive vertical elevations and depres- 

 sions, or to oblique thrusts and resiliences ? Or are there both 

 stationary and progressive oscillations ? 



The subject does not seem to have received much definite 

 investigation, although it finds incidental expression here and 

 there in geological literature. It is clear, however, that a deter- 

 mination of the stationary or progressive character of crust 

 oscillations must have an important bearing upon the various 

 hypotheses that concern the relations of the earth's crust to its 

 interior. It is obvious that preliminary to a study of these prob- 

 lems there must be dismissed from consideration those merely 

 apparent oscillations of the crust that are in reality but variations 

 of the sea level. It seems quite certain, however, that when 

 these are eliminated there remain a large class of true crustal 

 movements. The elucidation of these is extremely difficult and 

 would be greatly aided if it were known whether they are local 

 or migratory, and, if migratory, whether there are any general 

 laws governing the direction of their movements, their rate of 

 progress, etc. If migratory, do these undulations radiate from a 

 point of origin in all directions, like the wave circles induced 

 upon a liquid surface, or do they, like tidal waves, creep forward 

 in a single direction ? 



If we combine by free hypothesis the elevations and depres- 

 sions of the Pacific coast during the Pliocene and Pleistocene 

 times with those of the Mississippi basin and of the Atlantic 

 coast, it is not difficult to construct a procession of elevations and 

 . depressions creeping successively across the continent. Is such 

 a synthesis supported by any close definite data indicating pro- 

 gressive undulation, or is it merely an artificial combination of 

 selected data thrown into order arbitrarily at the suggestion of 

 an hypothesis ? This illustrates a class of questions whose solu- 

 tion presumably leads back to crustal and sub-crustal agencies. 



