OX THE SHORES OF THE ISTHMUS OF PANAMA. 41 



being more confined, any loss caused by evaporation 

 would be less readily replaced than that carried off 

 by evaporation from the open waters of the Pacific. 

 If, however, by the action of evaporation the level 

 of the waters of the Gulf of Mexico be depressed 

 below that of the adjacent parts of the Pacific, 

 and be, notwithstanding, higher than the general 

 level of the Atlantic ; then must the general level 

 of the Atlantic be lower than those parts of the 

 Pacific. 



If, then, the winds and evaporation be regarded as 

 the causes which determine such differences of level 

 as are at present under consideration; and, if cause 

 cannot be shown why, through the agency of the 

 winds and evaporation those parts of the Pacific ad- 

 jacent to the Isthmus of Panama should stand at a 

 higher level than the rest of the Pacific Ocean ; then 

 must it be contended that the level of the Pacific is 

 altogether higher than that of the North Atlantic ; 

 as a cause for which the winds and evaporation are 

 obviously inadequate. In fact, the winds and evapo- 

 ration must be discarded as comparatively trivial 

 forces, and altogether inadequate to cause any im- 

 portant difference in level between those parts of 

 the Pacific and Atlantic adjacent to the Isthmus of 

 Panama. 



We have said that westward pressure tends, 

 about the Isthmus of Panama, to raise the level of 

 the Atlantic and to depress that of the Pacific. And 



