ATLANTIC COAST TIDES* 

 By Mark S. W. Jefferson 



The tides of the eastern American coast are oscillations of the 

 shallow waters on the continental shelf communicated from the 

 swaying ocean heyoiid. 



The area must be subdivided into the coast proper, facing the 

 open waters of the shelf, and the shallow basins included behind 

 islands and banks. 



The continental shelf is a submerged platform alongour shores, 

 sloping so gently that it would appear flat to the eye if it were a 

 land surface, and margined eastward by the line of 100 fathoms 

 soundings. 



From Long island northward a line of banksrear their summits 

 to within 30 fathoms of the surface along the eastern margin 

 of the shelf, with deeper waters between them and the land. 

 Between these banks, however, are numerous deeper openings, 

 through which tidal movements are communicated landward 

 as well as over the shallow banks. 



Southward from Long island the descent of the shelf is beach- 

 like and uninterrupted from the shore to the line of 100 fathoms. 

 Only in the waters east of southern Florida do the Bahamas come 

 in to interrupt the descent to the ocean depths. This general 

 configuration is shown on the accompanying sketch (see p. 498), 

 where a broken line represents the 100- fathom line and the ap- 

 proximate boundary of the continental shelf, the dotted lines 

 inclose the banks, and the band of shading indicates the steep 

 slope to depths of 2,000 fathoms. Numbers indicate tide ranges. 

 The northern half of the shelf is seen to be wider than the south- 

 ern, besides being distinguished by the line of banks. 



Within this area lie the inclosed basins — Long Island sound, 

 the Gulf of Maine, and the Gulf of St Lawrence. They increase 

 in depth and size from south to north. 



TIDES ON THE COAST PROPER 



An examination of the whole coast line shows an intimate re- 

 lation between time and range of tide and the form of cross- 

 section of the continental shelf off each station. In a few cases 



* Extract from Thesis in research course in Geography at Harvard University. 

 34 497 



