HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 203 
PANAMA Dav. 
Although we have now passed from the Caribbean to the Pacifie, the 
continental section is not yet completed, for its features continue south- 
ward, twice as far, across the waters and islands of the 
Gulf of Panama. This great pouch-like indentation 
into the southern coast of the Isthmus of ' 
Panama, 100 miles long, is exceedingly à ih 
shallow, hardly reaching 50 fathoms in ҮШ 
depth until we cross an imaginary line Es 
drawn between the opposing headlands 
marking the entrance to the Gulf. (See 
Plate VL) Beyond this line, which is 
& continuation of the shores of the most 
southerly mainland bordering the Pa- 
| | cific, the submarine profile makes a sud- 
l) den plunge of from 50 to 1,800 fathoms 
k. or more. "Thus it will be seen that the 
bottom of the Gulf of Panama is really 
but a few feet below the present level 
of the sea, and a slight elevation would 
convert the whole bay into a rugged 
land area similar to that of the present 
mainland. 
Furthermore, this great gulf is marked 
by numerous islands and islets rising 
above this submarine platform of the 
bay. Some of the summits rise higher 
than that of Culebra, the so called con- 
tinental backbone. Тһе highest of the 
eleven pointed hills of Tobago Island is 
nearly a thousand feet in altitude (ex- 
actly 935 feet), while the adjacent To- 
baguilla is 710 feet. 
The intervening floor of the bay be- 
tween these islands and the mainland, 
only a few miles distant, is but seven fathoms (42 feet) 
in depth. Still farther out into the bay the group con- 
stituting the Pearl Islands present the same rugged Panamie topog- 
raphy, the points rising to various altitudes, some of them as high as 
600 feet. 
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