KNOWLEDGE OF EARTH STRUCTURE 183 



produced not only the subsidence of the Appalachian region 

 through the Paleozoic, but also, cotemporaneously, and as its 

 essential prerequisite, the rising of a sea-border elevation, or 

 geanticlinal, parallel with it ; and that both movements demanded 

 the existence beneath of a great sea of mobile rock." 



The recognition of regional warping as a major factor 

 in the larger structure of mountain systems, and the 

 expression of that factor in the terms geosyncline and 

 geanticline forms a notable advance in geologic thought. 

 Subsequent folding on a regional scale results in the 

 development of synclinoria and anticlinoria. Van Hise 

 has given these latter terms wide currency, but appar- 

 ently inadvertently has used synclinorium in a different 

 sense than that in which Dana defined it. Dana gave the 

 word to a mountain range made by the mashing and up- 

 lift of a geosyncline, Van Hise defines it as a downf old of 

 a large order of magnitude, embracing anticlines and 

 synclines within it; anticlinorium he uses for a corre- 

 sponding up fold. 12 Rice has called attention to this 

 change of definition, 13 but Van Hise's usage is likely to 

 prevail, since they are needed terms for the larger moun- 

 tain structure and do not require a determination of the 

 previous limits of upwarp and downwarp, of original 

 denudation and deposition. Furthermore, a geosyncline 

 in mountain folding may have one side uplifted, the other 

 side depressed and there are reasons for regarding the 

 folds of Pennsylvania, Dana's type synclinorium, as 

 representing but the western and downfolded side of the 

 Paleozoic geosyncline. Under that view the folded 

 Appalachians of Pennsylvania constitute a synclinorium 

 in both the sense of Dana and Van Hise. 



The Ultimate Cause of Crustal Compression. 



The next important advance in the theory of moun- 

 tains was made by C. E. Dutton who in 1874 published in 

 the Journal (8, 113-123) an article entitled "A criticism 

 upon the contractional hypothesis. " Dutton gives rea- 

 sons for holding that the amount of folding and shorten- 

 ing exhibited in mountain ranges, especially those of 

 Tertiary date, is very much greater in magnitude and is 

 'different in nature and distribution from that which 



