TAHITI. 



155 



We were of course very anxious to make careful measurements, and to ascer- 

 tain if possible the rate of growth of corals on that bank, as it would give a 

 growth of sixty years. While Captain Moser was engaged in placing his 

 instruments in position on the monument established by Wilkes, I recon- 

 noitred in the steam launch the 

 shoal, which is about half a 

 mile from the shore, and sounded 

 across it in all directions, and 

 carefully examined its surface 

 with a water glass. I was 

 greatly surprised to find that 

 the Dolphin Bank was really not 

 a coral bank. Only a few di- 

 minutive coral heads (Porites 

 and Pavonia) could be found on 

 it; none larger than my fist. 

 The surface of the bank was 

 covered with fragments of bro- 

 ken coral coated with Nullipores, and no corals were growing on the slopes 

 as they passed into deeper water. It was very evident that unless the 

 conditions have been radically changed in the past sixty years, no one had 

 carefully examined the surface of the Dolphin Bank, as nothing was said 

 either by Wilkes ' or Dana or the French naval officers of the condition of 

 the corals on the banks. In fact, this part of the shore of Tahiti, as well 

 as the whole of Matavai Bay (PI. 209), is, with the exception of a small reef 

 flat stretch at the extremity of Point Venus, covered with volcanic sand. 

 A more unfortunate selection could not have been made. 



A very heavy swell is always rolling over the bank, and even in moderate 

 weather is nearly on the point of breaking, so that it is difficult to remain 

 any length of time on the shallowest point of the bank, after it has been 

 found; Our soundings agreed with those of the charts within eighteen 

 inches ; as there is a considerable range of tide, it would always be difficult 

 to reduce them to the same plane without prolonged observations. 



1 Wilkes' Narrative, U. S. Ex. Ex., Vol. II. p. 40. 



Wilkes' Monument, Point Venus, Tahiti. 



