=Mountain Chains.=--The Sierra Nevada constitutes also a very important barrier to the diffusion of species. This is, however, broken by the passage of the Columbia River, and many species thus find their way across it. That the waters to the west of it are not unfavorable for the growth of Eastern fishes is shown by the fact of the rapid spread of the common Eastern catfish,[120] or horned pout, when transported from the Schuylkill to the Sacramento. The catfish is now one of the important food fishes of the San Francisco markets, and with the Chinaman its patron, it has gone from California to Hawaii. The Chinese catfish, described by Bleeker as _Ameiurus cantonensis_, was doubtless carried home by some Chinaman returning from San Francisco. In like fashion the small-mouthed black bass is now frequent in California streams, as is also the blue-green sunfish, _Apomotis cyanellus_, introduced as food for the bass. The mountain mass of Mount Shasta is, as already stated, a considerable barrier to the range of fishes, though a number of species find their way around it through the sea. The lower and irregular ridges of the Coast Range are of small importance in this regard, as the streams of their east slope reach the sea on the west through San Francisco Bay. Yet the San Joaquin contains a few species not yet recorded from the smaller rivers of southwestern California. The main chain of the Alleghanies forms a barrier of importance separating the rich fish fauna of the Tennessee and Ohio basins from the scantier faunæ of the Atlantic streams. Yet this barrier is crossed by many more species than is the case with either the Rocky Mountains or the Sierra Nevada. It is lower, narrower, and much more 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,[121] which is found in all suitable waters from Hudson's Bay to the head of the Chattahoochee.