142 REMARKS AND OPINIONS. 



sloping, and the edge less sharply marked lies 

 inider the water. It seems that the beds are de- 

 clivous in the interior, and that the upper beds do 

 not reach so far as those on which they rest. The 

 anchorages found in the Laguna of the groups, at 

 four, six, and eight fathoms' depth, protected by 

 the chief islands lying to the windward, are owing 

 to this declivity of the stony layer. The lead, 

 however, generally sinks at the inside, and along 

 the reef, from a depth of two to three fathoms im- 

 mediately to twenty or twenty-four, and you may 

 pursue a line in which on one side of the boat you 

 see the bottom, and on the other the azure-blue 

 deep water. 



A fine white sand of madrepore fmgments covers 

 the declivity of the dam, which is washed by the 

 water. A few kinds of branching madrepores, 

 or millepores, rise partially from this bottom, in 

 which they have fixed themselves, with roots of a 

 round form. Several others grow on the stone 

 walls of larger clefts, the bottom of which is filled 

 up with sand ; among these also the Tuhipora 

 mifsica, which we saw in a living state, and the 

 producers of which we recognized to be a polypus 

 of the form of a star of eight rays. Species which 

 cover the stone, or assume a lozenge form {Astrea) 

 are always met with in the constantly-watered 

 hollows of the bottom, next to the breakers. The 

 red colour of the reef, under the breakers, is 

 caused by a NulUpora^ which covers the stone 



