FORMATION OF CORAL REEFS AND ISLANDS. 243 



the left, and the west cape of Matavai harbor, on the right, 

 here reproduced, affords illustrations of this subject. 



a. The harbor of Papieti is enclosed by a reef about 

 three-fourths of a mile from the shore. The entrance through 

 the reef is narrow, with a depth of eleven fathoms at centre, 

 six to seven fathoms either side, and three to five close to the 

 reef. This fine harbor receives an unimportant streamlet, 

 while a much larger stream empties just to the east of the east 

 cape, opposite which the reef is close at hand and unbroken. 



b. Toanoa is the harbor next east of Papieti. The en- 

 trance is thirty-five fathoms deep at middle, and three and a 

 half to five fathoms near the points of the reef. There is no 

 fresh-water stream, except a trifling rivulet 



c. Papaoa is an open expanse of water, harbor-like in 

 character, but is without any entrance ; the reef is unbroken. 

 Yet there are two streams emptying into it, one of which is 

 of considerable size. 



d. Off Matavai, the place next east, the reef is inter- 

 rupted for about two miles. The harbor is formed by an ex- 

 tension of the reef off Point Venus, the east cape. There is 

 no stream on the coast, opposite this interruption in the reef, 

 except toward Point Venus, and at the present time the wa- 

 ters find their principal exit east of the Point, behind a large 

 coral reef, but a quarter of a mile distant. 



From such facts, it is evident that the growth of coral 

 reefs is not much retarded about the Pacific Islands by fresh- 

 water streams. "We cannot be surprised at the little influence 

 they appear to have exerted about Tahiti, when knowing that 

 none of these so-called rivers are over three feet in depth ; 

 and the most they can do is to produce a thin layer of brackish 

 water over the sea within the channels. 



e. The following figure of the harbor of Falifa, Upolu, 



