HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 171 
kept by Mr. Schaffer of the Panama Railway Company, the rainfall 
was 154 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 but 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 сап be seen upon the hydrographie charts 
of the Chiriqui 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 
