328 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



Dodo Pass the reef flat was, as on the nortli, covered with a number of 

 islands and islets, extending to Tagelib Pass and beyond to East Pass 

 (PI. 228, fig. 4). From Tagelib the reef flat is bare, the sea breaking 

 heavily upon it; it remains bare as far as the base of tlie small lagoon 

 which extends like a huge horn in a northeasterly direction from the 

 northeast corner of Arhno. 



On the west side of Arhno, near the south point, we encountered high 

 shingle dams, forming exceedingly narrow land rims, the outer sea face 

 and the lagoon being separated by a mass of rubble thrown up on the sea 

 face and washed, in part, towards the interior of the lagoon. 



A striking feature of Arhno is that the sea face of the islands on the 

 land rim of the northeastern part of the atoll is flanked by heavy shingle 

 (PL 181, fig. 1), similar to that which has been thrown upon the eastern 

 face of the atoll. 



In many places the high shingle beaches form isolated dams of con- 

 siderable length ; as, for instance, the immense dams of rubble on the sea 

 face of the secondary lagoons of Taritari, where the rubble has been thrown 

 to a height of at least nine feet. With the decomposition of this rubble 

 and broken fragments into sand, islands covered with vegetation have 

 been built on the line of the dam. At the northeast point of Arhno, 

 spits of rubble, similar to the sand spits so common in the gaps of the 

 atolls of the Marshall Islands, have been thrown out from the lagoon 

 face of the immense dam forming its eastern land rim. 



The small islets of the Marshall group which are not atolls or possess 

 no sinks, or where only slight depressions exist, must have been thrown 

 up on isolated peaks or ridges, as have secondary lagoons on extensions 

 of the faces of spits of such atolls as Likieb, Arhno, and Rongelab, That 

 is, beaches are thrown up on a shoal to a height of from twelve to fourteen 

 feet enclosing a circular sink, or an elliptical depression, or a longitudinal 

 trough, the existence of which has nothing to do with either elevation or 

 subsidence ; it is merely an open space left between a series of encircling 

 beaches. The sink is gradually filled with material thrown over the 

 beaches from all directions. Thus a low island is formed with a slight 

 depression or with a shallow lagoon, the land rim of which may become 



