I IO 



POPULAR SCIENCE MONTHLY 



Typical Bkidge of Substantial Character. Note the Absence of I'rominent Keystones. 



sometimes by a fourth. These watery mountains spread across the whole chan- 

 nel, and advance with a prodigious rapidity, rending and crushing everything 

 in their way. Immense trees are sometimes uprooted by it and sometimes whole 

 tracts of land are swept away. 



Tidal Currents in Rivers 1 

 There is no appreciable tidal effect in rivers due directly to the 

 tidal attraction of the sun and moon, but the tidal wave in a river is 



1 See G. H. Darwin, " The Tides," etc., Scribners, 1898. This contains also 

 an account of the Hangchow Bore based on Captain Moore's survey, to which 

 we shall refer later on. 



