HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 171 



kept by Mr. Schaffer of the Panama Railway Company, the rainfall 

 was 151 inches. The atmosphere is nearly always saturated with mist, 

 except in the dry season, during the months of January, February, 

 and March. During these months the rainfall is much greater than the 

 mean annual of the United States. It is hut natural that such enor- 

 mous discharges of rainfall acting through long centuries should produce 

 great erosion, and as a result the entire face of the country has been 

 etched by numerous streams, which, although short, are of great volume. 

 The discharge of the Chagres River, the drainage area of which does not 

 exceed 1,000 square miles, varies from 350 to 70,000 cubic feet per 

 second. 



Still further evidence of the fact that the present Isthmus is but a 

 remnantal and decaying land is the actual destruction now taking place 

 through marine erosion, which can be seen in operation along the 

 coasts. 



The effect of marine erosion npon the coast of the Caribbean is very 

 marked. While the tide does not exceed three feet in ebb and flow, it 

 is accompanied by a very choppy and persistent surf, (no doubt greatly 

 due to the strong trade winds,) which is constantly attacking and 

 carrying away the unconsolidated beds of the coast formations. Notable 

 instances of this action taking place are found in Limon and Manzanilla 

 Bays, where I could see evidence that great areas of the swamp land 

 had but recently been destroyed, are specifically cited on a succeeding 

 page. This effect is also shown in the tidal streams, the alternations 

 of ebb and flow resulting in the undermining and corrasion of the un- 

 consolidated banks. 



Perhaps the best illustration of the tremendous effect of this marine 

 erosion on the Caribbean side can be seen upon the hydrographic charts 

 of the Cbiriqui Lagoon. Here what was once a coastal plain between 

 Boco del Drago and Valiente Peninsula has been cut into numerous 

 islands. 



"Were I indulging in hypothetical geology it would be easy to recon- 

 struct a portion of the ancient Caribbean land which has been destroyed 

 by the action of the marine erosion, but it is not my province to enter 

 into such speculations at the present time. It is sufficient to say that 

 it is possible that a vast area of the former coast of the Caribbean coastal 

 land, as it existed in late Tertiary time of the Isthmian region, has been 

 planed away by this agency, now seen to be so actively in operation. 



Marine Erosion of the Pacific Coast. — The great difference between 

 the character of the tides upon the Atlantic and Caribbean shores is 



