6o2 Mr. mann’s freatife 
current, equally towards the two fides, where the velocity 
of the dream is the lead: in the whole fedlion. 
2diy, If the bed is irregular and winding, the line of 
greated current will be thrown towards one fide of the 
river, where its greated force will be exerted in propor- 
tion to the local caufes which turn it afide : in lliort turns 
of a river there will be a gyration, or turning round of 
the dream, by reafon of its beating againd the outer fide 
of the angle; this part will be corroded away, and the 
bottom near it excavated to a great depth. The matters, 
fo carried off, will be thrown againd the oppofite bank of 
the river where the current is the lead, and produce a 
new ground, called an alluvion. 
3dly., Inequalities at the bottom of a river retain and 
diminilli the velocity of the water, and fometimes may 
be fo great as to make them reflow : all thefe effects con- 
tribute to the fubfiding of fand, earth, and other matters 
thereon, which ceafe not to augment the volume of the 
obdacles themfelves, and produce lhallows and banks in 
the channel. Thefe in time, and by a continuance of 
the caufes, may become iflands, and fo produce great and 
permanent changes and irregularities in the beds of 
rivers. 
4thly, fbe percujfions of the center of the current againd: 
the fide of the bed are fo much the greater as they are 
made 
