68 MAYOR— ROSE ATOLL, AMERICAN SA^IOA. 



1 did not find upon the Rose Atoll reef rim a single specimen of 

 branched Acropora related to A. miiricata, nor did I see Acropora 

 arena fa or A. leptocyathus, which are dominant forms on the sea- 

 washed edges of reefs elsewhere in Samoa. 



Holothviria were fairly common, as were also small specimens 

 of the giant clam Tridacna, and among echini a few Cidaris and 

 black long-spined Diadciiia were seen; and the bright green seaweed 

 Caulcrpa was here and there found in the troughs between the 

 ridges of lithothamnium ; yet apart from the pink lithothamnium all 

 other organisms were a negligible factor on the upper surface of the 

 atoll rim. 



It is important to observe that among the hundreds of loose 

 boulders, or " negro heads," scattered over the fiat upper surface of 

 the atoll rim there are a few which still retain their connection with 

 the floor and project above it as "mushroom" rocks, thus indicating 

 either that the atoll rim has risen 6 to 8 feet or that sea level has 

 sunken to this extent. The evidence, however, supports the view 

 that sea level has become lowered, and not that the atoll rim has 

 arisen ; for there is no visible tilting of the rim, and, moreover, all 

 the volcanic islands of American Samoa are surrounded by a bench 

 of volcanic rock which is uniformly about lo feet above present high 

 tide level and is backed by volcanic sea cliffs, thus indicating that 

 these islands have remained stationary while sea level has become 

 lowered. 



In this connection it may be of interest to observe that with the 

 exception of Mangareva, which is volcanic, and Alakatea, which is 

 elevated, coral limestone, all of the atolls of the Paumotus exhibit 

 a bench of old limestone now several feet above present high 

 tide level. It will also be recalled that David and Sweet in their 

 account of the Geology of Funafuti^ conclude that in this atoll there 

 must have been either a land-elevation or a sea-sinking of at least 

 9 to lo feet. In 191 3 we observed a sea bench of about 3 feet 

 around both the volcanic and continental islands of Torres Straits. 



As there are fossil corals and lithothamnium in the highest parts 

 of the boulders and mushroom-rocks on the rim of Rose Atoll, it 



2 Funafuti Report, 1904, p. 84. 



