ON THE GEOLOGICAL AGENCY OF THE WINDS. 185 



rains, the fogs, and the dews.* Thus the great lakes of this con- 

 tinent would remain inland seas at a permanent level ; the salt 

 brought from the soil by the washings of the rivers and rains 

 would cease to be taken off to the ocean as it now is ; and final- 

 ly, too, the great American lakes, in the process of ages, would 

 become first brackish, and then briny. 



378. Now suppose the water-basins which hold the lakes to be 

 over a thousand fathoms (six thousand feet) deep. We know 

 they are not more than four hundred and twenty feet deep ; but 

 suppose them to be six thousand feet deep. The process of evap- 

 oration, after the St. Lawrence had 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 

 w^ater-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. 



379. Or let us take another case for illustration. Corallines 

 are at work about the Gulf Stream ; they have built up the Flor- 

 ida Reefs on one side, and the Bahama Banks on the other. Sup- 

 pose they should build up a dam across the Florida Pass, and ob- 

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

 connect Cuba with Yucatan, by damming up the Yucatan Pass, 

 so that the w^aters 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. The officers of the 

 United States ship Albany have run a line of deep-sea soundings 

 from west to east across the Gulf; the greatest depth they re- 

 ported was about six thousand feet. Subsequent experiments, 

 however, induce the belief that the depth is not quite so great. 



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 precipitation. 

 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 suffi- 

 cient 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 evaporating 



* The quantity of dew in England is about five inches during a year. — Glaishcr. 



