Chemical and Physical Papers. 77 



personally of many forest belts which have traveled outward for a 

 considerable distance in the last twenty years. The same is true 

 of the development of wooded blufPs. 



The origin of the different types of forest belts and patches may 

 be considered under the following heads: (1) The river- bottom ; 

 (2) the creek bottom; (3) the wooded bluff; (4) the ravine. 



T/ie River-bottom. — The main development of forest in the river 

 valley is along advancing sand-bars. On the inner side of the river 

 bends the low bar is often overflowed and covered with a rich sedi- 

 ment, On the edge of the bar, above the river-bed proper, there 

 usually grows up a belt of Sand-bar willow {Salix Jluvmtilis) 

 which often travels forward at about the same rate as the bar ad- 

 vances. The roots of this willow spread out beneath the surface 

 of the sand and send out numerous shoots, so that a very close 

 thicket is formed. The Sand-bar willow soon dies, but in the 

 meantime it is replaced by the Peach-leaf willow, and finally by the 

 Cottonwood. The cottonwood forest is the normal river-bend forest, 

 and is gradually replaced by the other trees of the river valley 

 which form the culmination flood-plain forest of the region. These 

 trees are as follows : Black walnut, White and Slippery elm, hack- 

 berry, Red mulberry, redbud, ccffee-bean. Honey-locust, and Green 

 ash. In an old forest which has gone through the normal develop- 

 ment, the trees enumerated above make up the bulk of the indi- 

 viduals, with here and there an isolated giant cottonwood, which 

 has escaped destruction. 



Sand-hills and ridges blown up by the wind support but a thin 

 stand of grass and other herbs, and in the blowouts and on the 

 newly formed ridges several shrubs, wliich are forest forerunners, 

 gain a foothold. The most important shrubs are Prunus watsoni 

 and Prunus anierrcana. Usually the first trees to come in are 

 Honey-locusts, coffee-beans, and, in the deep blowouts, cotton- 

 woods. 



Ravines opening into low river-bottoms sometimes lose their 

 channel before reaching the stream, and the soil thus covered with 

 sediment gives rise to a moist-ground forest. The first important 

 trees and shrubs are Sand-bar willow. Peach-leaf willow, and in the 

 lower places Cephalantfius. Finally White Elm, Green ash. Black 

 walnut and other trees take possession, and a normal forest is pro- 

 duced. 



Cut-off river meanders also frequently give rise to forests. The 

 old channel is gradually filled up with mud and sand, and, where 



