OSCILLATORY CHARACTER OF CONTINENTAL SEAS 375 



As to the possibility of the existence of deposit-prohibiting currents, 

 and of their efficiency as erosion agents, in geological ages wholly un- 

 represented by accessible deposits on the flanks and summits of interior 

 areas of uplift, no other evidence than that afforded by the fossils can 

 fairly be considered. The essential features of this evidence were brought 

 out in discussing the Black Eiver-Trenton submergences. Taken as a 

 whole, though it may be well to lay particular stress on the provincial 

 distinctness of the faunas (whether regarded as exactly contemporaneous 

 or not), the faunal evidence is unqualifiedly opposed to the suggestion of 

 current efficiency being responsible for discontinuties of sedimentation in 

 continental seas, except under such very unusual conditions as were 

 mentioned near the beginning of this discussion. 



Having, as I believe, fairly weighed Mr. Willis' suggestions concerning 

 marine scour and found them wanting on the unqualified evidence of 

 both the organic and the physical criteria, I feel justified in continuing 

 to regard agelong interruptions of marine deposition in continental 

 basins as indicating corresponding emergences. (See also pages 448-467.) 



The Stratigraphic Column 

 development of the american paleozoic column 



Review of the classifications of other author's. — Going no farther 

 back in the history of American stratigraphic classification than 

 1862, the year in which Dana issued the first edition of his Manual of 

 Geology, a work that in its successive editions may be fairly claimed to 

 express, though somewhat conservatively, the status and progress of the 

 science, the accepted major divisions of the Paleozic were as follows : 

 (1) Silurian age, divided into Lower Silurian and Upper Silurian, and 

 each of these into three periods, the former into Potsdam, Trenton, and 

 Hudson, the latter into Niagara, Salina, and Lower Helderberg; (2) 

 Devonian age, divided into five periods, Oriskany, Upper Helderberg, 

 Hamilton, Chemung and Catskill; and (3) Carboniferous age, with three 

 periods, sub-Carboniferous, Carboniferous and Permian. This classifica- 

 tion was essentially that of Hall, published a few years earlier in his Iowa 

 report, and less in accord with the classification now generally accepted 

 than were those published by De La Beche in 1851, and Lyell in 1855. 

 Both of these British authors recognized five major divisions, distinguish- 

 ing a Cambrian below and a Permian at the top. 



In 1875 Dana modified his classification by recognizing a Primordial 

 or Cambrian period at the base of the Silurian, the Canadian and Trenton 

 periods constituting the middle and upper parts of the Lower Silurian. 

 The Upper Silurian, Devonian and Carboniferous are the same as in 1862, 



