38 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



On the south shore (the lagoon shore) of the outer island this ledge projects 

 in an irregular outline from the shore, and in many places is completely 

 hidden by the overlying stratified recent beach rock or the recent breccia 

 and conglomerate. I was informed that at Kaukura there were great 

 outliers of old reef rock fully 17 feet above the general level of the lagoon 

 plateau. 



A section made across the land rim east of Avatoru Pass from the lagoon 

 side to the sea is quite simple. Starting from our anchorage in 9| fathoms 

 at a distance of about half a mile from the shore, the water shoals very 

 gradually to three or four fathoms, where we came across patches, some of 

 considerable size, of Porites, of Madrepores, and of Pocillipores, growing 

 either on the slopes of the outcropping reef flat or on its surface. 

 We then came to the base of the steep coral sand beach or coral shingle 

 beach from six to eight feet in height, at the base of which crops out here 

 and there the recent stratified beach rock or conglomerate. 



The lagoon beach to the east of Avatoru village is an excellent example 

 of the character of an inside beach of one of the larger atolls (PI. 6, figs. 

 1, 2). Tlie beach is steep, with a bench at a height of from five to six feet ; 

 below it the slope is covered with moderately fine sand made up of coral 

 and broken shells. The upper part of the shelf above the bench consists 

 mainly of broken shells, large fragments of recent corals, more or less 

 worn, and of fragments of old reef rock and old reef rock corals, the 

 latter derived from the disintegration and erosion on the lagoon side of 

 the edges of the same platform which crops out as the reef platform on 

 the sea face, and forms the underlying base of the lee land of the atoll. 

 This platform varies greatly in width ; usually it is much narrower on the 

 sea face of the land rim, being sometimes not more than 75 to 150 feet 

 wide (PI. 11), while on the lagoon side the old platform is at times more 

 than a mile wide. The shingle of coral and shells is weathered and thrown 

 up to the very top of the beach from seven to eight feet above low-water 

 mark ; it consists of pieces of coral shingle varying in size from a walnut 

 to that of one's fist, and on the slope of the shelf of pieces varying from a 

 half to two inches, intermixed with more or less coarse coral sand. At the 

 foot of the beach slope, near low-water mark, both above and also below 



