300 "ALBATROSS"' TROPICAL PACIFIC EXPEDITTOX. 



reef faces ; it is only when an unusually large block of coral forms the outer 

 edge at low-water mark that we may have a drop of four to six feet. 



The base of the sand dunes is flanked by a sort of beach rock conglomer- 

 ate composed of fine and coarse particles, small fragments or blocks of which 

 had been thrown up on the sea face of the dunes. 



We found at many other points on the west side of Menschikov sand 

 dunes overwhelming old and much-weathered coral heads near the head of 

 the reef flat, while on the outer part may run a ledge of higher blocks of 

 corals, some of which are still alive and have not been overwhelmed either 

 by sand or cut down by the action of the sea to the level of the reef flats, 

 as have the inner line of blocks. We found a large number of Echinoderms 

 living in the cavities between the corals. 



The mode of formation of the extensive flats we described at Taritari, on 

 the weather side of the atoll, is identical with that of the lagoon flats near 

 the openings and passes in the Marshall Islands. These flats are character- 

 istic of all of the atolls ; their existence has been more or less correctly 

 indicated and sketched out on the German charts of the group (Pis. 226, 

 figs. 5, 6, 9, 10 ; 227, fig. 3). 



Tengeli (PI. 227, fig. 2), another island on the west face of the land 

 rim of Menschikov, is in a somewhat more advanced stage than Gehh, 

 the island we have just described. Here the inass.of sand, coming from the 

 inner part of the lagoon, has overwhelmed the coral heads, and it is only 

 iiere and there, on the face of the reef flat, that we see an outcrop of the 

 coral heads. 



Between Mann and Torrutj Island a good pass exists ; on the lagoon 

 side of this gap a number of lines of secondary islands are formed on the 

 reef flat parallel to the outer island. These islands are separated by reaches 

 of blue water, forming two or three entrances into the lagoon from that face 

 of the island. 



From what I could ascertain of the depth of the lagoons in the Marshall 

 Islands, some of them are exceedingly shallow, as at Taongi (PI. 227, fig. 3) 

 and Namorik (PI. 226, fig. 10) ; in general they have a depth of from four- 

 teen to seventeen fathoms, though some of the larger lagoons reach a depth 

 of twenty to twenty-five fathoms. 



