30 



THE OPAL SEA 



Height of 

 tide wave. 



How the ^^® American continent. In the Indian Ocean 

 tide travels, j^ jg greatly retarded by island groups and nar- 

 row straits. In the North Atlantic it is broken 

 again by shoals, by pockets like the Gulf of 

 Mexico, and passes like the English Channel, 

 until its movement as a single effect can hardly 

 be followed. 



From its enormous mass and rapid move- 

 ment this tide wave might be thought to have 

 great height, but such is not the case. In the 

 Southern Pacific it does not average more than 

 from two to five feet, and that may be consid- 

 ered its normal height; but when a tide five 

 feet in height is driven against a shore at the 

 rate of one thousand or even one hundred miles 

 an hour, it can be easily imagined that there 

 would be a great rush of waters up the slope. 

 The eastern coast of North America which re- 

 ceives the full force of the Atlantic wave, has 

 a tide of from five to twelve feet; and its bays 

 and river mouths, where the water enters at 

 wide entrances and is gradually driven into a 

 narrow upper harbor, have a flood tide much 

 higher. At the mouth of the Bay of Fundy 

 the tide is eight feet in height; at its farther 

 end this same tide is wedged and pushed up to 

 a height of sixty feet or more. In the Bristol 

 channel the flood tides reach up forty feet. 



Wedged 

 water. 



