HOUINAL Gk GEOLOGY 
SEPTEMBER-OCTOBER, 1909 
CONDITIONS GOVERNING THE EVOLUTION AND 
DISTRIBUTION OF TERTIARY FAUNAS 
W. H. DALL 
U. S. National Museum, Washington D. C. 
xe 
The subject allotted me being “The Conditions Governing the 
Evolution and Distribution of Tertiary Faunas,” I may begin by 
stating certain propositions which, for the purposes of this discourse, 
may be assumed as axiomatic. 
t. A fauna is an assemblage of organic species populating a given 
area at one and the same epoch, and—allowances being made for 
the preferences of such minor groups as carnivorous, phytophagous, 
littoral, benthal, petricoline, and limicoline animals—having for the 
most part identical geographical distribution. 
2. We may regard it as indisputable that the properties of the 
environment shown to influence a living fauna, or to control its distri- 
bution, were capable in Tertiary? times of exerting an analogous 
influence on faunas now known chiefly by their fossil remains; and, 
conversely, if in a fossil fauna we are able to trace certain definite 
features, which in a living assembly would result from a particular 
environment, we are justified in concluding that the fossil fauna in 
«Dr. F. H. Knowlton’s article on “Succession and Range of Mesozoic and 
Tertiary Floras,’’ which should have appeared as No. X in this series, has never 
reached the Journal of Geology and does not appear, therefore in its proper place. 
Should the article be submitted later, it will be published. 
2 The author realizes that these factors may not be entirely applicable to the faunas 
of pre-Tertiary epochs. 
Vol. XVII, No. 6 493 
