870 Proceedings of the Royal Society 
deep fissures and narrow gulleys, running at right angles to the 
coast, which are being constantly widened by the action of the sea, 
and are often of considerable length. Frequently, when following 
a coast path, I have come unexpectedly, within the margin of the 
trees, upon the termination of one of these narrow gulleys, at the 
bottom of which, 10 or 12 feet below me, the water was rushing to 
and fro with each advancing and receding wave. The coral rock of 
these flats is much honeycombed on the surface, and its sharp 
cutting edges soon destroy a stout pair of hoots. It is extensively 
undermined by the sea, and, as might be expected, blow-holes are of 
common occurrence. They vary in size from the mere bubbling of 
air and water through a small hole in the rock to the grand spout 
which sends its foam 20 feet into the air. On this coast of St 
Christoval I have had my helmet blown off my head, while stand- 
ing without knowing it over one of these holes. They are of 
frequent occurrence on the coral limestone coasts of these islands. 
Besides the solvent action of rain on the elevated coral flats of 
the coast, numerous other agencies assist in the removal of the rock. 
On the raised coral flats of the north coasts of St Christoval, 
Nerita marmorata (Homb. & Jacq.) thrives in numbers just above 
the high water level. The calcareous excretions of these molluscs 
were to he observed in nearly every hole and crevice of the rock in 
this situation ; and it was evident to me that in this manner they 
increased in size the cavities into which they crept. 
On the south side of St Christoval I only became acquainted 
with the coast to the westward of the entrance of Makira Harbour. 
Here the sea border is of a different character. Lofty hills rise 
direct from the sea to a height of from 1000 to 1500 feet, and tall 
cliffs of ancient volcanic rocks start up perpendicularly from the 
deep water at their base. Lines of shore-reefs and elevated reef- 
flats, such as are found on the north side of the island, are not to 
be found here. In their place there are off-lying isolated coral 
patches lying from 5 to 10 fathoms below the surface, and rising 
with wall-like sides from deep water. On p. 867 I have given an 
explanation of the submerged condition of these and other similar 
sunken reefs. 
The Three Sisters . — Off the north coast of St Christoval lie the 
three small islands thus named. They may be briefly described as 
