THE GEOLOGICAL AGENCY OF THE WINDS. 289 



twenty feet deep ; but suppose them to be six thousand feet deep. 

 The process of evaporation, after the St. Lawrence 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 island 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 Eeefs 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 

 Mexico. 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 betw^een evaporation and 

 precipitation. If the former were in excess, the level of the 

 <jtulf waters would sink down until the surface exposed to the air 

 would be just sufficient to return to the atmosphere, as vapour, 

 the amount of water discharged by the rivers — the Missis- 

 sippi and others — into the Gulf. As the waters were lowered, 

 ihe extent of evaporating surface would grow less and less, until 

 Nature should establish 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. TJie formation of inland basins — a third process. — There is 

 still another process, besides the one already alluded to, by w4iich 

 the drainage of these inland basins may, through the agency of 

 the winds, 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 

 Df dry land instead of water for the winds to blow upon. Now 

 suppose that a continent should rise up in that part of the ocean, 

 wherever it may be, that supplies the clouds with the vapour 

 that makes the rain for the hydrographic basin of the great 

 American lakes. Wliat w^ould bo the result? Why, surely, 

 fewer clouds and less rain, which would involve a change of 



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