INSTABILITY IN STRATIGRAPHIC CLASSIFICATION 291 



for a spirit of concession and compromise in matters of detail and 

 method between the lithological stratigrapher and the stratigraphical 

 paleontologist. Neither should be asked to sacrifice important principles. 



POSSIBILITIES OF CORRELATION BY FOSSILS 



There are limits beyond which correlation can not go. Within a single 

 stratigraphic province, as, for instance, the Mohawkian area, extending 

 from Cincinnati southwestward to northwestern Alabama and southeast- 

 ward to the southwestern corner of Virginia, or, in the Silurian province, 

 embracing southern Indiana on the north and west middle Tennessee on 

 the south, satisfactory correlation is possible to the smallest units that it 

 is practical to map. And in such cases no other evidence than that af- 

 forded by the fossils is essential. But when it comes to correlating minor 

 stratigraphic units of distinct basins, then the fossils need the help of 

 other criteria. The fossils supply the first step in the process. They 

 give us a reliable clue as to the boundaries of the major divisions. 

 Finally, the principles of diastrophism fix these with greater precision and 

 supply data on which correlations of minor rank may be based. But with 

 no fossils at all it would be simply impossible to attain satisfactory re- 

 sults. Had not a Walcott found remains of Olenellus in the quartzitic 

 sandstones on the east side of the Appalachian Valley, many areas now 

 known to be lower Cambrian would still be classed as Medina; and had 

 not a Euedemann discovered certain Eurjrpterids in the Shawangunk 

 sandstone, we might never have been able to prove that this formation 

 also is not of Medina age. We might cite local successions of sandstone, 

 shale, and limestone differing in no physical respect from similar cycles 

 of sedimentation elsewhere that could never have been distinguished ex- 

 cept for the infallible clue given by a few or, may be, but a single fossil. 



On the other hand, the evidence of the fossils — often used by the pale- 

 ontologist with such confidence and finality against the conclusions of the 

 structural geologist that the rather disrespectful appellation of ^^autocrat" 

 may sometimes appear justified — is not an obvious quality of the fossils 

 themselves. The sequence of faunas as known today is the result of 

 long continued and laborious research in areas of undisturbed strati- 

 graphic succession. Faunal zone after faunal zone was located and their 

 respective relations to certain lithologic units noted. Thus piece by 

 piece the column has been built up. But the very foundation of the 

 training of the modem paleontologist, who is not merely a biologist, 

 makes him a good stratigrapher. Besides, there is no phase of diastro- 

 phism or of biology that he does not use or is not willing to use in the 

 improvement of his determinations. His training is broader and he mu?t 

 work harder than any other class of geologist. Yet the paleontologist 



