THE IMPENETRABLE SEA 



reaches of the Bay of Fundy are often completely drained 

 by the falling tide, so that vast areas of red mud are dis- 

 closed. Areas of fertile marshes are situated at the head 

 of the bay. The remains of a submerged forest show that 

 the land has subsided there, in the latest geological 

 period, nearly fifty feet. 



The Petitcodiac, which empties into Chepody Bay, at 

 the extreme north-west of the Bay of Fundy, is navigable 

 up to twenty-five miles for ships, and for twelve miles 

 farther at high tide. It is but one of many rivers which 

 empty into the Bay of Fundy which has a tidal bore — a 

 crest varying from three to six feet in height which 

 rushes up the river at certain times. Because of its high 

 tides and the many bores in its rivers, the bay is noted 

 for its navigational perils, especially in its upper 

 reaches. 



The gravitational pull of the earth upon its own waters 

 is millions of times greater than the pull of the sun and 

 the moon combined, yet the sun can draw the earth's 

 waters a little way towards it with a force which operates 

 across ninety-three million miles of intervening space, 

 while the moon (infinitely smaller than the sun, yet more 

 powerful in its pull because it is so much nearer to the 

 earth) exercises its invisible power across a distance of 

 nearly a quarter of a million miles. 



In the open oceans the water piled up into a tidal wave 

 by the moon's attraction (affected to varying degrees by 

 the pull of the sun) follows the moon as it apparently 

 circles the earth. This true tidal wave (which must not 

 be confused with tidal waves caused by earthquakes or 

 other ocean-floor disturbances) must be measured not in 

 feet or miles but in hours. It is a tidal wave roughly 

 twelve hours and twenty minutes in length (half the time 

 that it takes for the moon to circle the earth — the 

 ''circling" being from our viewpoint, of course). The 

 height of the heaped-up water is called "the tidal range". 

 Over the wide oceans this averages about three feet high, 



86 



