MAYOR— ROSE ATOLL, AMERICAN SAMOA. 65 



Fortune, which cruised continuously around the island, there being 

 no anchorage, were the only insects we observed. 



The upper surface of the atoll rim which encircles the lagoon is 

 a hard smooth-floored flat, with but little loose sand upon it, and in 

 most places it is awash at low tide, although in others it projects as 

 a ledge about a foot above low tide of the reef tides. 



This hard, smooth surface of the atoll rim is veneered every- 

 where by a layer of Hthothamnium, as is characteristic of the wave- 

 washed surface of offshore and barrier reefs. The condition over 

 the fringing reefs of the Pacific is quite different, for here loose 

 fragments are washed inward from the seaward edge and backed up 

 against the shore. Thus the whole surface, excepting only the 

 wave-washed outer edge, is covered with small loose fragments 

 which could not remain upon an atoll rim or a barrier reef, for they 

 would soon be washed off into the lagoon. This loose nature of the 

 material forming the shoreward parts of fringing reefs at once dis- 

 tinguishes them from offshore reefs. Professor W. M. Davis's 

 attempt, following Darwin, 1842, to institute a class of " offshore 

 fringing reefs" is not justified, the structure of the two forms of 

 reefs being widely different. As a matter of fact, reefs along 

 shores are either barrier reefs or fringing reefs, and one is never 

 in any doubt in distinguishing the one from the other. 



Hundreds of large blocks of limestone, of the sort called "negro 

 heads " on the barrier reef of Australia, lie scattered over the flat 

 wave-washed rim of Rose Atoll. These loose boulders are quite 

 uniformly about 5^ feet high, and only when tilted are they any 

 higher. In addition to the loose boulders there are a few others 

 which are mushroom-shaped and still remain attached to the floor 

 of the atoll rim, of which, indeed, they form an integral part. One 

 of the most remarkable of these mushroom-rocks lies to the east- 

 ward of Rose Islet, and is supported upon so slender a pedicel that 

 it would seem as if the next storm must cause it to topple over. In 

 many places over the flat wave-washed floor of the atoll rim one 

 finds remnants of pedicels which once supported " mushrooms.'' In 

 addition, some of the boulders have become secondarily cemented to 

 the floor of the flat by the growth of hthothamnium around their 



