HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 170 
made by this elevation once extended over at least what is now Man- 
zanilla Day and Limon Day, and probably out seaward some distance, 
Hence it is equally certain that since these late sediments were thus 
elevated into land the former seaward extension of the coast has been 
partially destroyed and its area diminished by the destructive surf 
erosion. 
That the Isthmian region was much narrower than now when these 
swamps deposits were below sea level is very evident, especially when we 
consider that similar phenomena occur on the Pacific side for at least 
four miles inland from the present margin of Panama Bay. The waters 
of the two oceans now forty-five miles apart, were then fifteen miles 
nearer together. Let not those who believe that the two oceans were 
recently united across the Isthmus interpret this former restriction of 
the Isthmian land as demonstrative of their theory, for it can be shown 
that when these swamp levels were submerged the two oceans were 
still separated by a land barrier of even greater height than that of 
to-day. 
SUBSEOTION 1.— Coton то Воло. 
Leaving the depot at Colon the railway first passes the swampy land 
of the lower end of the island, and then crosses the narrow strait known 
as Fox River, which connects Limon and Manzanilla Bays. 
The Monkey Hill Base Levelled Terrace. — Beyond this swamp а low line 
of hills is met. These are lobed and cut into many individual members, 
but the eye recognizes readily that their summits, less than a hundred 
feet in height, are the remnants of a once continuous bench or level. 
Біогвв 2. Monkey Hills, near Colon. 
The physiography of the Monkey Hills is of great interest. Their 
uniform summit level, traceable a few miles eastward, parallel to the coast, 
clearly represents an ancient base levelled surface, probably what was the 
low coast border when the Mindi swamps were below the waters of the sea. 
Although this old level has been subjected to later erosion, so much so 
that it is now dissected into numerous mammillary hills, there can be 
no misinterpretation of the fact that their summits were once a con- 
tinuous plain. We may own that this old plain once included Lion and 
Tiger Hills to the southward, now separated from the Monkey Hills 
proper by a vast area of swamp. I am inclined to believe, however, that 
