DEPRESSIONS IN THE EARTH'S SUR- 

 FACE. 



(Read before the Cincinnati Society of Natural History, Oct., 1888.) 



The contents of oceans and seas hold in solution 

 a variable amount of chloride of sodium and other 

 saline matter, the degree of salinity depending largely 

 upon the relative aqueous waste through evaporation. 

 If a kettle of brine be boiled till all the water has es- 

 caped in steam, the utensil will contain the saline in- 

 gredients as a crystalline incrustation at the bottom. 

 The dissipated steam represents ordinary vapor rising 

 from the surface of a pool, pond, lake, or sea, through 

 the heating agency of the Sun. The watery particles 

 floating in the atmosphere are at length condensed 

 into clouds and precipitated as rain, returning to the 

 earth what was seemingly lost through evaporation. 

 Thus the circulation of water goes on ; and the gen- 

 eral level of water in basins having no outlets is main- 

 tained. 



In ordinary ponds and lakes the water is confined 

 by dams, dykes, and natural barriers till it attains a 

 height equal to the lowest point in its surroundings. 

 Then as much will be discharged as the inlets furnish. 

 If, however, a pool or pond evaporate more water in 

 dry weather than the feeders supply, the outflow 

 ceases, and the shore line sinks or retreats within a 

 smaller circumference. Now, if this shrinkage con- 

 tinue, the basin must at length become dry, or nearly 



(148) 



