Rocky Mountains, seems not to be an element of any importance 

 in this connection. Of the fish which cross this chain, the most 

 prominent is the brook trout {Salvelimis fontiiialis)^ which is 

 found in all suitable waters from Hudson's Bay to the head of 

 the Chattahoochee. A few other species are locally found in 

 the headwaters of certain streams on opposite sides of the 

 range. An example of this is the little red " fall-fish " {Notrobis 

 riibricroceiis Co'po), found only in the mountain tributaries of the 

 Savannah aiid the Tennessee. We may suppose the same 

 agencies to have assisted these species that we have imagined 

 in the case of the Rocky Mountain trout, and such agencies 

 were doubtless more operative in the times immediately follow- 

 ing the glacial epoch than they are now. 



The passage of species from stream to stream along the 

 Atlantic slope deserves a moment's notice. It is, under present 

 conditions, impossible for any mountain or upland fish, as the 

 X.ro\xtox \h.Qva{\\Qv'st\\nvah {Cottiis richai'dsoiii Agassiz), to cross 

 from the Potomac river to the James, or from the Neuse to the 

 Santee, by descending to the lower courses of the rivers, and 

 thence passing along either through the swamps or by way of 

 the sea. The lower courses of these streams, warm and muddy, 

 are uninhabitable by such fishes. Such transfers are, however, 

 possible farther north. From the rivers of Canada and from 

 many rivers of New England the trout does descend to the sea 

 and into the sea, and farther north the whitefish does this also. 

 Thus these fishes readily pass from one river basin to another. 

 As this is the case now everywhere in the North, it may have 

 been the case farther south in the time of the glacial cold. We 

 may, I think, imagine a condition of things in which the snow- 

 fields of the Alleghany chain might have played some part in 

 aiding the diffusion of cold-loving fishes. A permanent snow- 

 field on the Blue Ridge in western North Carolina might render 

 almost any stream in the Carolinas suitable for trout, from its 

 source to its mouth. An increased volume of colder water 

 might carry the trout of the head-streams of the Catawba and 

 the Savannah as far down as the sea. We can even imagine 

 that the trout reached these streams in the first place through 

 such agencies, though of this there is no positive evidence. For 



