122 SCIENCE SKETCHES. 



broken, — as in New York, in Pennsylvania, and in 

 Georgia there are several streams which pass 

 through it or around it. The much greater age of 

 the Alleghany chain, as compared with the 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,^ 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 head- 

 waters of certain streams on opposite sides of the 

 range. An example of this is the little red '' Fall- 

 fish," ^ found only in the mountain tributaries of 

 the Savannah and the Tennessee. We may sup- 

 pose 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 imme- 

 diately following the glacial epoch than they are 

 now. Professor Cope calls attention also to the 

 numerous caverns existing in these mountains, as 

 a sufficient medium for the transfer of many spe- 

 cies. I doubt whether the main chains of the Blue 

 Ridge or the Great Smoky can be crossed in that 

 way, though such channels are not rare in the sub- 

 carboniferous limestones of the Cumberland range. 

 The passage of species from stream to stream 

 along the Atlantic slope deserves a moment's 

 notice. It is, under present conditions, impos- 

 sible for any mountain or upland fish, as the Trout 

 or the Miller's Thumb,^ to cross from the Potomac 



1 Salvelinus foittinalis. 2 ]\Totropis rubricroceus Cope. 



3 Cottus richardsoni Agassiz. 



