on Rivers and Canals . 589 
that this ftate of things muft contribute far more to the 
fubftdency of mud and all other matters brought down 
by the waters in canals, than can be the cafe in rivers 
whofe currents conftantly flow. 
35. I do not fuppofe that thefe inconveniencies can 
have yet manifefted themfelves by any very fenfible ef- 
fects in the many new canals and lluices lately conftrudted 
in England; but as the fame caufes do not ceafe to aft 
more or lefs every where, the effects which neceffarily fol- 
low from them will likewife become more and more fen- 
lible, unlefs continual care be taken to prevent them. 
The waters of all rivers and canals are from time to time 
muddy: their ftreams, particularly during rains and 
floods, carry along with them earth and other fub- 
ftances which fubfide in thofe places where their cur- 
rents are the leaft, whereby their beds are continually 
railed : fo that the fucceflive increafe of inundations in 
rivers, and of unfitnefs for navigation in canals, when 
they are neglected and left to themfelves, is a natural and 
neceflary confequence of the ftate of things, which no 
intelligent perfon can be at a lofs to account for; and yet 
I have known whole countries remain in this habitual 
ftate of negligence to their very great detriment. 
36. Having thus fliewn the principal accidents which 
rivers and canals are liable to, with the caufes of them, I 
Vol. LXIX. 4 H fhall 
