STRATIGRAPHIC TAXONOMY 577 



was impossible. Any of these possible conditions, if they occurred, as it is 

 believed they did, must have had a decided effect on the composition of 

 faunas that invaded the inland seas. 



Considering the many possible conditions that are competent to cause 

 breaks in the faunal record of local stratigraphic sequences, whose magni- 

 tude is in nowise proportionate to their respective time values, the vary- 

 ing import, hence the inadequacy, of fossil evidence as a primary factor 

 in the construction of a detailed geological time scale is apparent. The 

 only possible basis for this scale lies in the stratigraphic relations of the 

 beds containing the fossils and in the movements which have occasioned 

 the shifting of the seas in which the beds were laid down and in which 

 the fossil organisms lived when conditions were favorable. The remains 

 of the latter are endowed with taxonomic attributes only when their 

 stratigraphic relations have been determined; and at that, except in a 

 broad and generalized wa}^, the application of the life sequence thus 

 worked out is limited by provincial boundaries. A new sequence must 

 be worked out for each of the other provinces. 



The stratigTaphic taxonomist, therefore, must be first and always a 

 stratigrapher. But, so I may not be misunderstood, I shall add that a 

 geologist can not be a self-competent stratigrapher unless he is equipped 

 with a considerable w^orking knowledge of fossils. It is not required of 

 him to know that a certain guide fossil is a Hebertella and not a Dinor- 

 this, or that the species which was formerly called Orthothetes suhplanus 

 is now referred to under the name Schuchertella subplana. Such changes 

 are in systematic biology and have no vital effect on stratigraphic tax- 

 onomy. What he needs is the ability to discriminate closely between 

 allied species and faunas and to recognize the individual forms and their 

 associations when he sees them again. 



Whatever the cause of the faunal change, be it great or small, local or 

 general, it probably was occasioned by some crustal deformation, and 

 movements of the lithosphere necessarily were accompanied by corre- 

 sponding displacements of the strandline. It is therefore by the correla- 

 tion of these displacements, which involves the use of all the criteria — 

 the physical no less than the organic — that we finally establish the se- 

 quence of marine deposits and define the stratigraphic units, whose classi- 

 fication is the chief object of this work. 



BAftlH OF PROPO^^ED REVTSITOX OF fiTPATIG R.\PHJC T.WOyOMY 



Discussion of the factors. — The criteria and principles of correlation 

 have been discussed at length in preceding parts. It will have been noted 

 that in estimatino- the relative values of the several criteria and methods 



