I034 FRESH-WATER BIOLOGY 



growth of weeds; little fluctuation during the year in the volume 

 of the stream or in the character of the water. 



"Limestone streams usually yield more species than streams 

 flowing over sandstone, and either more than the streams of regions 

 having metamorphic rocks. Sandy bottoms usually are not favor- 

 able to fishes. In general, glacial drift makes a suitable river 

 bottom, but the higher temperature usual in regions beyond the 

 limits of the drift gives to certain southern streams conditions 

 still more favorable. These conditions are all well reahzed in the 

 Washita River in Arkansas, and in various tributaries of the Ten- 

 nessee, Cumberland, and Ohio; and in these, among American 

 streams, the greatest number of species has been recorded. 



''The isolation and the low temperature of the rivers of New 

 England have given to them a very scanty fish fauna as compared 

 with the rivers of the South and West." 



Agassiz says concerning New England: "In this isolated region of 

 North America, in this zoological island of New England, as we 

 may call it, we find neither Lepidosteus, nor Amia, nor Poliodon, 

 nor Amblodon, nor Grystes, nor Centrarchus, nor Pomoxis, nor 

 Ambloplites, nor C alliums, nor Carpiodes, nor Hyodon, nor indeed 

 any of the characteristic forms of North American fishes so com- 

 mon everywhere else, with the exception of two Pomotis, one 

 Boleosoma, and a few Catostomus.^'' 



Continuing, Jordan says: 



"Of the six hundred species of fishes found in the rivers of the 

 United States, about two hundred have been recorded from the 

 basin of the Mississippi. From fifty to one hundred of these 

 species can be found in any one of the tributary streams of the 

 size, say, of the Housatonic River or the Charles. In the Connecti- 

 cut River there are but eighteen species permanently resident; and 

 the number found in the streams of Texas is not much larger.** 



"The waters of the Great Basin are not rich in fishes, the species 

 now found being evidently an overflow from the Snake River when 

 in late glacial times it drained Lake Bonneville. This postglacial 

 lake once filled the present basin of the Great Salt Lake and Utah 

 Lake, its outlet flowing northwest from Ogden into Snake River. 

 The same fishes are now found in the upper Snake River and the 



