of Edinburgh, Session 1885 - 86 . 
873 
reached the surface. Further on in this paper I shall show that 
large atolls probably assume their characteristic form below the 
surface, as pointed out by Mr Murray. 
I was not able to visit the other two islands. They have, how- 
ever, the same general appearance and about the same elevation. 
Lieut. Malan, who coasted round both of them and landed on 
Malaulalla, tells me that they are counterparts of Malaupaina, the 
southern island which I have above described at length. In Malau- 
lalla he found a lagoon shut oh apparently from the sea, but he 
did not notice one in the northern island of Alita. On the north- 
east coast of the island last mentioned, he observed a line of cliff 
of coral limestone 30 to 40 feet in height. 
Santa Anna . — The shore-reefs, which skirt the coast of the upraised 
atoll of Santa Anna, vary in width from 150 to 600 yards, according 
to the steepness of the land; and the average submarine slope to the 
100 fathom line ranges from 6 degrees to rather over 20 degrees. 
The reef-flats between the tidal levels are traversed by fissures 
2 to 5 feet broad, which extend far beyond the breakers, and may 
usually be traced from the surface by the white sand that has 
collected in them. On the west coast the shore-reefs enclose a 
remarkable circular lagoon, 700 to 800 yards in width, which has a 
depth of 16 to 17 fathoms, and affords a snug anchorage for ships. 
It is known as Port Mary. 
On the south shore of this lagoon, a dark red compact rock has 
been exposed at the bottom of some holes, a foot in depth, which 
have been excavated for water by the natives in the rock of the 
reef-flat. The same rock occurs as embedded masses in the surface 
of the reef-flat on the east coast, where it contains enclosures of 
coral rock and other debris. I also found it lining the sides of a 
vertical fissure in a coral limestone cliff, where it was from 1 to 2 
inches thick. This rock effervesces with an acid; but, as I learn 
from Mr Murray, it is mainly composed of a red ochreous material, 
probably deposited from water that has found its way through 
fissures and cavities in the coral limestone. Its exposure on the 
surface of the reef-flat (near its inner edge) may probably be due to 
the solvent action of the sea water which overflows the flat towards 
high tide. The circumstance of its lining the sides of a fissure in 
a coral limestone cliff is very suggestive of its origin. Professor 
