1 88 SEA AND LAND 



connected, tliat one ma)- journey in a small boat nearly all 

 the way without being exposed to the open sea. 



The lai^oon bar element in our shoredlne topography is so 

 important, both from the [)oint of \'iew of science and that of 

 economics, that the reader should attain a clear understanding 

 as to the mannt,'r in which these bars are formed. We shall 

 therefore examine in a somewhat detailed wa)' the process 

 of construction. Whenever these reefs abound next the 

 coast, we find on examining charts of soundings which depict 

 the shape of the bottom of the neighboring sea that the coast 

 is bordered by a wide belt of shallow w^ater which extends 

 as a gradually inclined plane, declining toward the open 

 ocean with a descent of from five to ten feet to the mile, its 

 surface covered with tolerably fine sand, mingled with the 

 debris accumulated by the marine life which inhabits the 

 ocean floor. From a line commonly lying from fifty to one 

 hundred miles from the coast, this broad, gently sloping con- 

 tinental shelf suddenly declines into deep water, its outer 

 margin often having a slope of one hundred feet or more 

 to the mile. It is clearly recognized by geologists that this 

 continental shelf is in the main made up of debris worn from 

 the land which has been distributed over the sea-floor by the 

 action of currents and waves, operating through a number 

 of geologic ages, during whicli the shore, although occasion- 

 ally rising and sinking in slight oscillations, has maintained 

 nearly its present position. 



Wherever this continental shelf is well developed beneath 

 the sea we are likely to find that a portion of the terrace 

 built during periods when the coast was somewhat lower 

 than at present extends inland in the form of broad, slightly 

 rolling, sandy plains. Such an emerged portion of the con- 



