282 THE ZOOLOGIST. 



one feels as if in some enchanted land. But the great feature of the group 

 is the birds'-nest caverns, which as a rule open into the sea, the entrance 

 being below high-water mark ; fortunately I visited them at spring tides, 

 and had plenty of leisure to examine each cavern at low water during two 

 days. At the south end of the largest island stands a " nine-pin " of grey 

 marble 870 feet high, almost separated from the rest. It is hollow, like 

 a huge extinguisher, and the polished light blue and yellow sides of the 

 interior seem to point to its having been hollowed by the swell of the sea, 

 which on entering the cave would probably expend its force vertically, the 

 mouth of the cave being open to the direction of the strongest seas. This 

 sea-stack forms the western point of a nearly circular cove, 360 yards in 

 diameter, which runs back into the island, and the sides of the cove rise 

 steeply though not perpendicularly from it. At the head of the cove is a 

 perpendicular wall of rock over which can just be seen the 1000-foot 

 summit in the distance. At half-tide a tunnel, passable for a canoe, opens 

 under the wall of rock at the head of the cove, but a ship's gig can only 

 enter within an hour of low-water spring tides. This tunnel has a roof 

 covered with large stalactitic knobs except at its narrowest part, where it is 

 apparently scoured smooth by the action of the tidal rush. It is about 

 250 feet long, and 4 feet deep at low water (the rise and fall of the tide 

 being 16 feet), and is covered with dripping marine life, corallines, small 

 corals, Comatulse, sponges, and sea-horses. Passing through this sub- 

 marine passage, one emerges into another circular crater-shaped basin with 

 perpendicular sides. This basin is only open to the sky; caves here and 

 there enter it, some of which may perhaps lead by long tunnels to other 

 basins. Water was running freely into it from the foot of the cliffs in 

 several places as the tide fell, showing that water spaces existed, and 

 strauge gurgling sounds as of air taking the place of water could be heard 

 now and again. There were hardly any signs of the place being frequented 

 by man, except here and there the worn ropes of birds'-nest climbers. It 

 was either not the season for the Swallows, or they had deserted the islands, 

 for none were seen. A little reddish guano was noticed in some of the 

 caves. There can be but little traffic through the tunnel by which we 

 entered, for the delicate growth on its sides was hardly injured. On the 

 west side of the northern large island a lofty cavern is connected at half-tide 

 with another nearly circular basin of about the same size as that we have 

 just described, but in this case the basin also opens into the sea on the east 

 side of the island. After contemplating the cliffs that surround these 

 basins, the general circular contour of the ridges of the islands, the under-, 

 mining action of the sea at the water-line, which causes in some places an 

 overhang of 20 to 25 feet, and the softening of the marble surface of the 

 cavern roofs by moisture, the conviction gradually forces itself on the mind 

 that these circular basius were themselves at one time the floors of huge 



