286 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



Millepores are the most abundant of the corals within the lagoons of the 

 Marshall Islands. In addition to Millepores, Porites, and the other larger 

 corals, which have already been mentioned, we collected Pavonia and 

 Fungia on the reef flats of Jaluit, and also a very peculiar Millepore, 

 different from any we had found elsewhere. The flats of the lagoon, both 

 on the eastern and on the western faces, are covered with Nullipores, 

 wherever coarse coral sand or coral shingle exists. On the lagoon face 

 of the land rim corals are quite abundant, as well as on the slopes 

 of the sand spits, to the north of the entrance to Jaluit. When the 

 coral heads reach the surface of the flat, they are overwhelmed by sand, 

 Nullipores begin to grow upon the dead materials, and little by little 

 they become covered, forming an inner coral reef flat similar to those 

 we have observed both on the inside and outside reef flats in other groups. 

 Following the lagoon slope, tlie corals disappear gradually towards deep 

 water, and at a depth of from sixteen to twenty fathoms we find only 

 patches of Nullipores and wide lanes of sand separating the few diminu- 

 tive heads still left. 



The average depth of the Jaluit lagoon varies from eighteen to twenty-five 

 fathoms, although here and there a deeper hole occurs. Large stretches of 

 the lagoon are comparatively shallow, having undoubtedly been filled up 

 from the weather side ; we can see how a smaller lagoon might readily 

 have been filled from the sand and shingle blown in over the outer land 

 rim during the prevailing trades. This filling up of the lagoon by sand 

 and shingle from the outside is a prominent feature in the Marshall Islands ; 

 it modifies to a considerable extent the width of the flats adjoining the 

 land rim. 



From our anchorage in nine fathoms came up a block of worn coral, 

 probably blown over the shingle dam into the lagoon from the outer 

 sea face. We found this to be a common feature on many of the islands 

 of the Marshall group, where the sea often breaks over the narrow outer 

 land rim, carrying large blocks of coral, which are deposited in lanes 

 along the lagoon slope of the land rim between the lines of outliers of 

 higher buttresses of harder breccia. This was perhaps better seen in Arhno 

 than in any other island of the group. 



