Natural History of District of Columbia — McAtee 73 



more strongly, must they have influenced the migrations, 

 settlements, industries, and character of the aboriginal mon- 

 archs of the Potomac waters and woodlands." 46 



The Fall Line as a Barrier. 



The fall line has importance as an actual barrier to the 

 spread of the fauna of the streams which cross it, since 

 they are uniformly characterized by abrupt descent. The 

 following illustrates this influence: Of the 80 species of 

 fishes known to be native to the region of the District 

 of Columbia, 8 which ascend the river to spawn are stopped 

 either by Little Falls or Great Falls. Fourteen others are 

 so dependent upon Coastal Plain conditions that they never 

 ascend the river even as far as the falls. In other words, 

 more than one-fourth of the native fish fauna is confined to 

 the Coastal Plain. Three species of fishes, namely, the brook 

 trout, trout perch, and Millers thumb, appears to be con- 

 fined to waters above the fall line. 



These various categories of species are given in full in 

 the following lists. What effect, if any, the fall line 

 has upon the distribution of other aquatic creatures is 

 unknown. 47 



Salt water fishes coming within the Washington area. 



Carcharhinus obscurus Leiostomus xanthurus 



Brevoortia tyrannus Menticirrus saxatilis 



Stolephorus mitchilli Chaetodipterus faber 



Cyprinodon variegatus Gobiosoma bosci 



Tylosaurus marinus Opsanus tau 



Siphostoma fuscum Prionotus carolinus 



Orthopristus chrysopterus Achirus fasciatus 



Fishes ascending river to Little Falls. 



Acipenser sturio Pomolobus mediocris 



brevirostris pseudoparengus 



aestivalis 



44 The American Anthropologist, Vol. II, 1879, pp. 233-234. W. J. McGee. 

 " Except for a few reptiles and batrachians previously cited. 



