RANGIROA. 39 



it, crop out bands of recent beacli rock (PI. 9), stratified and dipping at a 

 slight angle towards the lagoon ; between the patches of beach rock are 

 heads of old reef rock, either as boulders which had been separated from the 

 lagoon edge of the old reef rock ledge and thrown up on the beach slope, or 

 still attached to the ledge, large pieces of which occasionally crop out inland, 

 but usually so hidden and covered by the surrounding fragments of recent 

 beach rock and fragments of corals that it is difficult to decide whether they 

 are part of the ancient reef rock ledge or have been thrown up by the sea 

 from the lagoon face of the old ledge of the island. 



From its highest point the beach slopes inland, and forms the outer dam 

 of a shallow sink in which fresh water collects. This lagoon sink (PI. 205) 

 is better developed in other islands, and will be described elsewhere. In the 

 rear of the village, to the eastward, the sink becomes a small shallow pond 

 which furnishes a large part of the fresh-water supply of the natives. On 

 the northern side of the sink the ground rises again, is undulating, and is 

 composed mainly of beach rock, the interstices being filled with coral shingle 

 and sand, which extends to the southern face of the high coral sand and 

 shingle beach facing the sea. The top of the outer sea beach is in places 

 fully 15 feet high, and is, like the inner lagoon beach, composed of coral 

 sand at the lower part of the slope, and of coral shingle towards the top. 

 The shingle extends inland in a comparatively gentle slope for quite a 

 distance, and finds its way between the cocoanut and low trees and shrubs 

 forming extensive broad lanes entirely devoid of vegetation. Isolated shrubs 

 often begin to grow on the sea face of the outer beach ; they increase soTne- 

 what towards the top of the beach, and form usually quite a thick growth 

 at or immediately behind the summit. The vegetation consists of many of 

 the same plants found on the Fiji reefs, and which are as a whole character- 

 istic of all the Pacific coral reef islands. - 



At the base of the Outer beach extends the shore platform (Pis. 8, 11, 12), 

 the underlying bed of which consists of old tertiary coralliferous limestone 

 more or less concealed by stretches of recent beach rock. The shore plat- 

 form at this part of Eangiroa varies from 75 to 150 feet in width, and is 

 flanked on its very outer edge by a ridge of Nullipores and of Pocillipores ris- 

 ing from two to four feet above the general level of the shore platform, which 



