642 Mr. mann's Treat if e 
is ia extenfive plains next the Tea; with regard to the de- 
clivity thereof alone , but not at all with regard to the ve- 
locity of the current there, which is often very great 
from the comprelTion and impulfion of the upper waters, 
as has been repeatedly fhevvn above muft be the cafe 
(N° 29. 38. 43. 72.). 
Second rate or clafs. Molt artificial canals in flat coun- 
tries, made for the ufe of navigation ; efpecially thofe in 
the Dutch and Auftrian Netherlands. 
Third rate or clafs. The river Trent; the Scheld and 
the Lys below Ghent; the Ifere and the Iprelee below 
Fort Knock in Flanders ; many rivers in the territories of 
Bologna and Ferrara in Italy; the river Meander in Na- 
tolia; and innumerable others in flat countries. 
Fourth clafs. The Thames; the Lys and the Scheld 
above Ghent in Flanders ; the Senne, the Dyle, and the 
Demmer,inBrabant; the Seine and the Somme in France; 
the Nile and the Niger in Africa; the rivers of St. Law- 
rence below Lake Ontario, the Oroonoko, the river of 
Amazons, and the rivers of Paraguay, in America. 
Fifth clafs. The Severn and Oufe in England; the 
Loire and Garonne in France; the Tagus, the Guadiana, 
and the Guadalquivir, in Spain ; the Po and the Tiber in 
Italy; the Meufe, the Rhine, and the Elbe, in Ger- 
many; the Weiffel, the Neifter, the Bog, and the Nieper, 
in 
