290 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



the unrest preceding a revolution. What shall we do to direct it toward 

 the promotion of our science? 



DUAL NOMENCLATURES 



As a result of my investigations I am opposed to a dual nomenclature, 

 or, indeed, to any scheme tending to divorce paleontology from stratigra- 

 phy. The study of fossils apart from their stratigraphic relations is 

 pure biology. With geologists the study of fossils should be a means to 

 a definite end, and that end the elucidation of the geologic history of our 

 earth. Geologic time should be measured by stratigraphic units, not by 

 the indefinite duration of successive but overlapping dominant types of 

 life. The time scale was not built up of life units, but of stratigraphic 

 units. Indeed, the only competent means of estimating geologic time is 

 based on ratios of deposition and on other considerations that are equally 

 distinct from biologic investigations. The geologic time scale, therefore, 

 is an essential feature of geology and not of biology. 



The lithologic scale, like any f aunal scale, is necessarily a local affair. 

 In other words, both scales are founded on factors that are more or less 

 strictly local in their typical development and subject to great variation 

 when pursued beyond these areas. N'either, therefore, is capable of sup- 

 plying data for a positive standard. So far as I know, there is but one 

 possible standard by which geologic events and sedimentary rocks may be 

 classified, and that is by time units — in other words, the chronologic 

 standard. 



MUTUAL CONCESSION 



It is evident that the remedy for the present difficulties lies not in 

 divorce, but in mutual concession and adaptation to prevailing conditions. 

 Faunal, diastrophic, and lithologic criteria are complementary, and each 

 kind may and sliould be used to check the other two. T^one of the three 

 classes of evixlence is competent by itself to insure a refined and true 

 classification of geologic time, l)ut l)etween them we may ho})e to construct 

 one. Let us reconstruct, or rather amend, our stratigraphic columns so 

 that they shall indicate all well defined lithologic boundaries as Avell as 

 the important faunal changes and the broader crustal movements that as 

 a rule caused both. 



Further, let us draw the various boundaries as nearly as possible in 

 accord with the composite evidence of all classes of criteria. I should 

 not object to considering even such non-geological matters as exigencies 

 of mapping. Often a lithologic boundary could be drawn just as well 

 or better at a line indicated by diastrophism or by a sharp faunal change 

 as at the ]")lane selected by the geologist without regard to either of these 

 criteria. There is need for closer cooperation, and, more important still, 



