§ 538. THE GEOLOGICAL AGENCY OF THE WINDS. 989 



(six thousand feet) deep. We know they are not more than four 

 hundred and twenty feet deep ; but suppose them to be six thou- 

 sand feet deep. The process of evaporation, after the St. Law- 

 rence has gone dry, might go on until one or two thousand feet 

 or more were lost from the surface, and we should then have 

 another instance of the level of an inland water-basin being far 

 below the sea-level, as in the case of the Dead Sea ; or it would 

 become a rainless district, when the lakes themselves would go 

 dry. Or let us take another case for illustration. Corallines are 

 at work about the Gulf Stream ; they have built up the Florida 

 Keefs on one side, and the Bahama Banks on the other. Suppose 

 they should build up a dam across the Florida Pass, and obstruct 

 the Gulf Stream ; and that, in like manner, they were to connect 

 Cuba with Yucatan by damming up the Yucatan Pass, so that the 

 waters of the Atlantic should cease to flow into the Gulf of Mex- 

 ico. What should we have? The depth of the marine basin 

 which holds the waters of that Gulf is, in the deepest part, about 

 a mile. We should therefore have, by stopping up the channels 

 between the Gulf and the Atlantic, not a sea-level in the Gulf, but 

 we should have a mean level between evaporation and precipita- 

 tion. If the former were in excess, the level of the Gulf waters 

 would sink down until the surface exposed to the air would be 

 just sufficient to return to the atmosphere, as vapor, the amount 

 of water discharged by the rivers — the Mississippi and others, 

 into the Gulf As the waters were lowered, the extent of evapo- 

 rating surface would grow less and less, until Nature should es- 

 tablish the proper ratio between the ability of the air to take up 

 and the capacity of the clouds to let down. Thus we might have 

 a sea whose level would be much farther below the water-level 

 of the ocean than is the Dead Sea. 



538. There is still another process, besides the one already al- 

 The formation of in- ludcd to, bv which the drainage of these inland ba- 



land basins — a third . , ., n a ' i i 



process. sius may, through the agency oi the wmds, have 



been cut off by the great salt seas, and that is by the elevation 

 of continents from the bottom of the sea in distant regions of the 

 earth, and the substitution caused thereby of dry land instead of 

 water for the winds to blow upon. Now suppose that a conti- 

 nent should rise up in that part of the ocean, wherever it may be, 

 that supplies the clouds with the vapor that makes the rain for 



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