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POPULAR SCIENCE MONTHLY. 



1,200, 1,500 or even in places to 2,000 fathoms. These depths are 

 reached at from two to five miles beyond the hundred fathom line. 



Eising from the floor of the sea some ten or twelve miles to the 

 southwest of this oval plateau is another much smaller one, which 

 would still be some 150 or 200 feet under the surface were the sea 

 to recede, as we have imagined, thirty feet. This is known as the 

 Challenger Bank. 



Ten miles beyond this is another similar plateau of about the 

 same size and height, called the Argus Bank. These two banks are in 

 reality a part — two detached peaks, as it were — of the great submarine 

 mountain of which the Bermuda Islands are the visible summit. For 



Fig. 7. Road Cutting near Hamilton. 



while the floor of the ocean sinks within five miles to about 1,500 

 fathoms, these plateaus are separated from each other and from the 

 Bermuda plateau by less than half that depth. 



The present land area of all the Bermuda Islands is composed of 

 calcareous rock which varies from a loose sand to a firm, hard, semi- 

 crystalline limestone that resounds to the blow of the hammer. What 

 underlies this, no one yet knows. The deepest excavations — those for 

 the new Navy Yard docks at Ireland Island — have not disclosed any 

 other kind of rock. The numerous deep cuts for roads (Fig. 7) and 

 the quarries which are met with in all parts of the islands tell the same 

 story. The rocks are composed of wind-blown calcareous sand. This 

 sand, contrary to what was formerly supposed, is not composed of 

 broken down corals. These are present only in small proportion, the 



