GEOLOGIC VERSUS LITHOLOGIC 241 
basis of tame scales, meaning graduated measures of time involved 
in either earth or life history. With Mr. Willis, the writer 
believes that much further investigation is necessary before 
complete adjustment of the time scales of geology and of pale- 
ontology can be made. In that condition lies no ground for the 
assumption that the geologist may not use paleontologic evi- 
dence at any time in accordance with the best knowledge of that 
time in deciphering the geologic record and in choosing forma- 
tion units for its cartographic representation. Doctrines of catas- 
trophism and special creation have yielded to the theory of 
evolution. A precise diagnostic value for a fossil in taxonomy 
is no longer claimed. But we still have a chronology of geol- 
ogy. We are now better informed than ever before as to the 
sequence of geologic events and as to the actual value of fossils 
to the geologist in all his researches. 
The knowledge that life has been continuous, that faunas 
and floras migrate, that shore lines migrate, shows that time divi- 
sions of exact synchronous value can never be established upon 
either faunal changes or lithologic character of sediments alone. | 
What the basis of the future time scale of geology will be can- 
not now be safely predicted. That is a matter which does not 
materially affect the problem under discussion. 
’ The task of the geologist mapping a given province is to 
express the facts of geologic development there. He may know 
that his stratigraphic divisions are not to be accurately correlated 
with those of distant provinces. His province has its own his- 
tory and his units of mapping, call them as you will, are to be 
discriminated primarily for the practical expression of that his- 
tory. He knows that in the main the broader correlations with 
the history of other provinces will hold good, and he should 
express correlations indicated by all the evidence known. 
The fact, now commonly recognized, that some faunas or 
floras cannot be used to establish the exact time equivalence of 
the beds containing them, in widely separated areas, does not 
seem to the writer to in the least warrant the conclusion that all 
correlation on fossil evidence is at present undesirable or unjus- 
tifiable. 
