FLUVIATILE. 251 



lowing the narration of this, the most recent chapter in 

 geological history. 



Among the most obvious of Eecent Formations are those 

 produced by the action of rain and rivers. Whatever the 

 winds and rains and frosts loosen and disintegrate, the 

 stream carries onward and downward to lower levels. 

 Were there no great rivers, the debris worn from the moun- 

 tains would accumulate mainly along their bases, but the 

 runnels gave it to the streams, the streams by their union to 

 the river, and the river carries it forward to be scattered over 

 the plains, to be deposited in lakes, or borne out to the 

 depths of the ocean. Geologically speaking, what is strictly 

 Fluviatile is laid down by the streams and rivers along their 

 courses ; and there is not a river in the world that does not 

 present, in some portion or other of its course, patches of 

 meadow-land, holmes, dales, and other flats, that have been 

 formed by the debris carried down by its current. These 

 alluvial flats are generally very heterogeneous in their com- 

 position loamy and clayey silts, sand, gravel, and shingle, 

 with here and there the imbedded but often imperfectly 

 preserved remains of terrestrial plants and animals. In 

 course of ages, as the river deepens its channel, and cuts its 

 way from side to side down the valley, the older of these 

 flats will stand higher and higher above the current ; and 

 thus it is that along most rivers there are sets of terraces 

 marking the heights at which they formerly ran, and the 

 levels over which they spread their inundating waters. It 

 is usual to arrange these terraces into higher river-gravels 

 and lower river-gravels the former of vast antiquity, and 

 rarely containing organic remains, and the lower of more 

 recent origin) and containing the remains of plants and 

 animals, some of which have long since become extinct in 

 the regions where their relics now occur. It is from the 



