Geologic Correlation.— Ward. 35 
the upper; and when the notion of age was once introduced as the 
equivalent of succession, it was no wonder that correspondence 
in succession came to be looked upon as correspondence in 
age, or contemporaneity; and, indeed, so long as relative age 
only is spoken of, correspondence in succession ‘s correspondence 
in age; it is relative contemporaneity. 
But it would have been much better for geology if so loose and 
ambiguous a word as ‘‘contemporaneous” had been excluded from 
her terminology, and if, in its stead, some term expressing simi- 
larity of serial relation, and excluding the notion of time alto- 
gether, had been employed to denote correspondence in position 
in two or more series of strata. 
In anatomy, where such correspondence of position has con- 
stantly to be spoken of, it is denoted by the word ‘homology and 
its derivatives; and for geology (which after all is only the anat- 
omy and physiology of the earth) it might be well to invent some 
single word, such as, ‘‘homotaxis” (similarity of order), in order 
to express an essentially similar idea,” 
The term ‘‘homotaxis”, thus introduced into geologic terminol- 
ogy, has been widely accepted, and is now in constant use, even 
by those who have not taken the trouble to inquire how it origi- 
nated, The geologist considers the stratigraphical and lithologi- 
cal relations and the paleontologist the related organic forms. 
As regards the latter class of workers, they are, I believe, agreed 
that two deposits should be considered homotactic* when their 
floras or faunas show a sufficiently large number of identical or 
closely allied species, or contain to a considerable extent the 
same types of life. 
I fully share with Dr. Newberry the view that fossil plants 
may be made of great value in the correlation of geologic strata, 
and also that when properly understood there will remain no con- 
flict between animal and vegetable fossils. The difficulty has all 
along been that the science of paleobotany is in an unsettled and 
unorganized state, and that correct principles have been wanting 
for the application of paleobotanical data. It is not claimed that the 
science has advanced to the point where its usefulness is at its highest 
stage; it is still as it were inits infaney. Nevertheless a sufficient 
body of facts now exist to make it a useful aid to geology. 
*This seems the proper adjective form, and not “homotaxial” as some 
authors write it. 
