Wind and tide greatly alter the strength of these currents due to difference of density, and the surface outflow may either be stopped or, in the case of the belts, actually reversed by a strong and steady wind.
In some instances travelling belts or creepers have been adopted, which deliver the coal with a reduced amount of breakage, but this application is not common.
Farther west two narrow belts of timber, consisting mostly of stunted post oak and black jack, and known as the Eastern and Western Cross Timbers, cross the prairies southward from the Red river, and a low growth of mesquite, other shrubs and vines are common in the eastern half of the Prairie Plains.
The river banks are lined with belts of dense forest, in which useful timber occurs.
Its shores are swampy and desolate and show considerable belts of saline incrustations with the fall in its level.