DESCRIPTION OF THE EXPEDITION. 149 
elevation to have been less than about 80 feet. The island, however, proved to be 
decidedly lower in the centre than on the sides, indeed quite basin-like, with its highest 
points on the rim, about 20 yards back from the cliffs. Further, there is a shelf at the 
low-tide level of 40 to 60 yards in breadth, which we can only regard as having been 
formed by the action of the waves on the land behind. This gives an additional diameter 
to the island of 100 yards in any line, and it may be that some of its higher parts have 
been removed. In fact, before elevation we could picture an atoll about a mile in 
diameter, its rim awash, enclosing a small lagoon of at least 5 to 6 fathoms in depth. 
Fig. 40. 
View on the shore at St. Pierre. 
Rough coral-rock with bushes of Pemphis acidula and boobies (Sula piscator) overhead. 
At most parts the cliffs are crowned with old gnarled bushes of Pemphis (fig. 40). 
Inside is a dense mass of small trees— Hibiscus, with masses of red flowers; Pésonia, 
with stunted stems never able to reach above the general level of 20 feet or so; and the 
_ tanghain, the famous poison-tree of Malagasy natives. The latter presented an extra- 
ordinary spectacle as of a forest of bare stems; it is completely deciduous, while most 
tropical trees gradually lose and replace their leaves. Other plants were of the regular 
- species which can stand the guano. Of birds, the booby (Sw/a piscator) was breeding in 
_ every tree, an immense guano-forming colony. 
After steaming around St. Pierre and sounding on each side, proving only the 
existence of particularly steep slopes, we proceeded to run a line of soundings to 
_ Alphonse, which with Frangois and Bijoutier forms a little group, 150 miles to the north 
of Providence. Unfortunately at the second sounding the machine which we were using, 
an old one on the starboard bow, split one of its sides off when reeling in after a sounding 
of 
