Joseph Barrell. 265 



published a series of three papers on the "Relative 

 Geological Importance of Continental, Littoral and 

 Marine Sedimentation" in the Journal of Geology. 



In these papers he sets forth a quantitative view as to 

 the relative importance geologically of these three types 

 of sediments, and the criteria for separating them. It 

 is a study of facts already assembled in the geologic 

 literature, but always from their original sources. Fur- 

 ther, it is the application of changing and cyclic geog- 

 raphies in their relation to stratigraphy, with the em- 

 phasis on the fact that by no means all of the sediments 

 are of marine origin. Among other things he develops 

 the criteria for discerning subaerial delta deposits, and 

 he shows that such deposits attain their greatest de- 

 velopment after epochs of mountain-making unaccom- 

 panied by notable uplift of the continental platforms. 

 He also emphasizes the cyclic relations between conti- 

 nental and marine sedimentation in geologic history. 

 The wide and cyclic significance of mud-cracks in asso- 

 ciation with other features indicating flood-plain deposits 

 is discussed at length and applied to the interpretation 

 of Proterozoic deposits in Montana and the Grand 

 Canyon of the Colorado. 



The significance of desert deposits becomes very 

 striking when one notes that one-fifth of the present land 

 surface is desert tracts. And Barrell estimates that the 

 subaerial deposits of piedmont waste, of continental 

 basins, and of deltas cover about one-tenth of the 

 emerged continental surfaces. Adding these "to the esti- 

 mate of the deposits of arid climates would give a fifth 

 of the land surface as mantled by continental forma- 

 tions." The lands in the course of the geological ages 

 are, however, warped and elevated into mountain ranges, 

 so that the geological record "should show a far less 

 proportion of these and superficial land deposits." On 

 the other hand, basin and delta deposits should be quan- 

 titatively as great as those laid down upon the floor 

 of the epeiric seas. 



Having developed the principles of sedimentation for 

 continental and shallow-water marine deposits, Barrell 

 applies them in 1907 to a late Mississippian formation 

 in the paper "Origin and Significance of the Mauch 

 Chunk Shale." Here are presented the significant facts 

 regarding this formation, gathered from the literature 



