The strongest instance of cataracts, resembling the ancient ones which connected the lakes of nearly all the great rivers of the globe, is seen in the fall of Niagara. That cataract is an epitome of the falls of all other streams. The Niagara River conducts the water of Lake Erie, by a channel 33 miles long, to Lake Ontario, 300 feet below it. At the Great Fall the river plunges about 150 feet into a chasm which it has hollowed out from the soft stone between the two lakes. The cataract was formerly seven miles below its present location, and has been observed to be steadily working backward since its discovery. In the distant future it will, doubtless, wholly disappear, as all others have done. For the Niagara is merely a striking instance of a principle once universal, but which merely worked itself out on a smaller scale. The more fragments of rock and mountain debris were swept along, the sooner were the primitive falls rent away by the wash and the percussion, and the development of the middle course completed. The places of transition which lie between the higher dry basins and the lower ones are still to be traced in almost all rivers; not by great waterfalls, which belong only to the upper course, but by simple rapids. They are more or less characterized by narrows, with steep, rocky banks, where, doubtless, cataracts existed in the primitive times. They are recognizable by this feature, that they are uniformly alike, and distribute their force equally on both sides of the river. Examples may be found on both sides of the Rhine, in the narrows between Bingen and Bacharach; on the Elbe, from Tetshen to Shandau, Dresden, and Meissen. In these places the rivers have a very tortuous course, and there are whirls and rapids (rapides, sauts, of the French; saltos, randales, of the Spanish; schewerin of the Russians) which impede navigation. In these localities the entire aspect of nature is changed, and the landscape becomes exceedingly beautiful. Here we find ancient narrow roadways; here are places of great historic interest, and of great interest to the naturalist, assuredly not of accidental origin, but in close connection with the development of the river bed, and in close analogy with all places of transition from highland to lowland.