BASELEVELING AND ITS FAUNAL SIGNIFI- 
CANCE, WITH ILLUSTRATIONS FROM 
SOUTHEASTERN UNITED STATES. 
CHARLES C. ADAMS. 
In considering some of the peculiarities of the fauna of the 
southeastern United States I wish to call attention to certain 
principles that are fundamental to an understanding of the 
present distribution of many forms of life, especially those of 
land and fresh-water. Especial stress is laid on the relation of 
physiographic changes, and baseleveling in particular, to faunal 
changes and to the differentiation of land and fresh-water 
animals.! 
The necessity of correlating the results of baseleveling, and 
river histories in particular, with the distribution of habitats 
and their fauna, was very emphatically impressed upon me in 
connection with some studies upon the Pleuroceridz of south- 
eastern United States. This relation was clearly demonstrated 
to me when I learned that the former course of the Tennessee 
River from Chattanooga was direct to the Gulf via the Coosa- 
Alabama system. Having thus become fully convinced of the 
great biological significance of the baseleveling factors, it was of 
considerable interest that I later learned that Woodworth (94) 
had already appreciated this significance. 
/ Ina general way, this relation of physiography to topographic 
: and geographic distribution has been well understood, but such 
\ Studies need to be carried out in more detail. The geologists, 
from their familiarity with the physiographic processes, seem 
to have had a better appreciation of this relation than zoólo- 
gists. Woodworth (94) has fully realized in a detailed way the 
Influence of the baseleveling processes upon faunal changes. 
1I am under obligations to Messrs. Salisbury, Hayes, and — aS per- 
T ion to use their figures and to Prof. E. A. Birge of the Wisconsin . and 
atural History Survey for the loan of the cuts for Figs. b ? and 3. 
