DISTRIBUTION OF REEFS. 137 
Pacific Ocean. 
The west coast of South America is known to be without coral reefs 
even immediately beneath the equator; and the seas of the Gala- 
pagos also grow no coral. The northward deflection of the coral 
boundary line, as shown, accounts for their absence. In the harbour 
of Callao (the seaport of Lima), the temperature is sometimes down to 
59° or 60° F., and at the Galapagos, Captain Fitzroy found the waters 
in September to fall often to 62° F., and once to 583° F. This month, 
it should be observed, cannot be the coldest of the year. In the bay of 
Panama, coral is reported to occur, but there are no reefs.* 
The coast to the north, as far as latitude 21° N., is within the 
warm limits, but without reefs. In Captain Colnett’s voyage, allusion 
is made toa beach of coral sand on one of the Revillagigedo Islands, in 
latitude 18°; beside this statement, I have met with no allusion to 
corals on any of the islands off the Mexican coast. The paucity of 
corals in this region may perhaps be owing, in some degree, to the 
fact that the tropical currents of the ocean flow mwestward instead of 
eastward ; and, consequently, they prove an obstacle to the distribu- 
tion of polyps to this coast from the islands of the Pacific. Moreover, 
the cold currents which pass the Galapagos form an impassable 
barrier between the Paumotus and Mexico. 
Between the South American coast and the Paumotus are two 
rocky islands, Easter or Waihu, and Sala-y-Gomez, both of which 
are without reefs. 
The Paumotus commence in longitude 130° W., and embrace eighty 
coral islands, all of which, excepting about eight of small size, con- 
tain lagoons. Besides these, there are, near the southern limits of 
the archipelago, the Gambier Islands, and Pitcairn’s, of basaltic con- 
stitution. The former, in 23° S., has extensive reefs; aout the latter, 
in 25° S., there are some growing corals, but no proper reefs. 
The Marquesas, in latitude 10° S., have but little coral about them ; 
and this is the more remarkable, as they are in close proximity to the 
Paumotus. But their shores are, in general, very abrupt, with deep 
waters close to the rocks. An island which, before subsidence has 
commenced, has some extent of shallow waters around, might have 
very bold shores, after it had half sunk beneath the waves. This 
* Jour. Roy. Geog. Soc. i. 69, on the Isthmus of Panama, by J. A. Lloyd. 
t Captain Beechey mentions that at forty-one fathoms, near Sala-y-Gomez, he found 
a bottom of sand and coral. 
35 
