MUSEUM OF COMPARATIVE ZOOLOGY. 9 
TOPOGRAPHY OF THE BOTTOM IN THE PANamio REGION. 
There çan be no more striking contrast than exists between the 
topography of the two sides of Central America. The Atlantic side? 
with the great inland seas of the Gulf of Mexico and Caribbean, and the 
great submarine banks extending from Yucatan, Honduras, and Vene- 
zuela, while on the Pacific side (Plate IIT.) the continental slope is steep, 
the 2,000 fathom line often coming within 100 miles of the coast line. 
(See Plates V. to IX.) The 100 fathom line, with the exception of the 
stretch forming the Bay of Panama, and a comparatively narrow conti- 
nental shelf along a part of the shore from Costa Rica to Tehuantepec, 
is within a few miles of the shore as far as the southern entrance of the 
Gulf of California, where it broadens out again to take in the Tres Marias 
group of islands. The 500 and 1,000 fathom lines are parallel with the 
100 fathom line, forming a very abrupt slope from Ecuador to the Gulf 
of California, except along the stretch between Cape Mala and Tehuan- 
tepec, where the distance between those curves is somewhat greater 
(Plate IIL), but still so slight as not to alter materially the prevailing 
steepness of the continental slope. In this same stretch the 1,500 
fathom line is from three to four times as distant from the 1,000 fathom 
curve as it is off the coast line extending from Panama to Ecuador, and 
from Tehuantepee to Cape Corrientes ; at the mouth of the Gulf of Cali- 
fornia, the 1,500 fathom line extends across the opening of the Gulf of 
California, coming in again close to Cape San Lucas. 
The rise upon which Malpelo (Plate VI.) is situated is bounded by 
the 1,500 fathom line (Plate IIL), and separated by a channel with 
over 1,700 fathoms of water from the Columbian and Ecuadorian coasts. 
And again the same curve forms a gigantic comma-shaped figure, tak- 
ing in Cocos Island (Plates III. and V.) and the Galapagos group; it 
is separated from the 1,500 fathom line off Mariato Point by over 1,600 
fathoms, and from the Malpelo Bank and Ecuadorian coast by over 
1,800 fathoms. (See Plate III.) The course of the 2,000 fathom line 
shows how very uniform is the depth of the floor of the Pacific beyond the 
1,500 fathom curve. The rise to the Galapagos is most gradual close to 
the islands, and the different islands of the Revilla Gigedo group, varying 
in distance from 300 to 500 miles from Cape San Lucas, form steep peaks 
suddenly rising from a comparatively level oceanic floor of an average 
depth of about 2,000 fathoms (see Plate IIL), which is nearly the 
1 See Figs. 55-59, Three Cruises of the “ Blake.” 
