6o2 THE POPULAR SCIENCE MONTHLY. 



ages, from the old "sawyers" that have bowed before the current 

 with rhythmic regularity perhaps for centuries, to the freshly-felled 

 monarchs still bearing their green leaves of the season. 



But the fact of chief interest is the presence of trees on the brink 

 of these eroded walls, whose still living and healthy trunks are laid 

 bare to a depth of several feet below the present surface of the 

 ground. In some cases the subterranean portion occupies as many as 

 four or five feet of the base of the trunk, descending through a num- 

 ber of distinct strata. But even at much greater depth there are 

 frequent and unmistakable relics of ancient forests long since de- 

 stroyed, or, as it were, buried alive. At depths of ten or twelve feet 

 below the present surface, old stumps, with roots and remains of trunks, 

 are brought to light by the inroads of the river. The trees which 

 these represented must have been buried deeper and deeper, in the 

 same manner as existing ones are proved to be undergoing burial, until, 

 unable longer to perform the functions of circulation, they died, and 

 all decayed except these deeply buried parts. Sometimes even these 

 are gone, and naught remains beyond a reddish stain against the ver- 

 tical wall to mark the spot where once there flourished upon the then 

 surface of the valley a large and healthy tree (see Diagram No. IV). 



The method thus far described of studying the mode of formation 

 of the river-valley is that of analysis — the observation of the action 

 of the water in disintegrating it. But we may also employ the method 

 of synthesis, and study the manifest process of valley-building which 

 takes place simultaneously. The river is always loading up on one 

 side, and unloading on the other. The deepest part of the river near 

 the high banks, as it sweeps round the great bends, is also the swiftest. 

 The current grows slower and slower in the direction of the opposite 

 shore, and at the same time the water grows more and more shallow, 

 until at last a sand-bar is reached gradually rising out of it. If this 

 proves to be the mainland, the case is simple, and we will first consider 

 this simple case. This sand-bar was formed at the last period of high 

 water in the spring and early summer. It therefore consists of sand 

 only, without vegetation. It may have a width of fifty or a hundred 

 feet when it ceases, and a distinct rise occurs, with a little terrace of 

 sand, thickly covered with seedling willows, all belonging to one species 

 {Salix longifolia, Muhl.), and bearing no other vegetation. The sand 

 is still damp, being saturated with water from the river. This land is 

 two years old. A short distance farther back another similar terrace 

 is reached, bearing a thicket of this same willow, but it is now two to 

 four feet high, and fruit-bearing. The land is here three years old. 

 Another remove brings us to a third terrace, having larger willows and 

 some other vegetation, such as is not injured by periodical floods flow- 

 ing over it. This four-year-old soil is darker in color and firmer. It 

 may complete the river-bed proper, or there may be still another ter- 

 race. As we recede from the river, these old river-bed marks become 



