34 "ALBATEOSS" TROPICAL PACIFIC EXPEDITION. 



Between Tiputa and Avatoru Pass (PI. 4, fig. 1) the outer islands are 

 flanked on the sea side with steep coral sand beaches alternating with 

 reaches of large boulders (Pis. 4, fig. 2; 13, fig. 1) extending on the 

 inner face of the shore platform to the foot of the sand beach or reaching 

 across the low cuts into the lagoon (Pis. 8 ; 9, fig. 1 ; 12, fig. 2 ; 13, fig. 2). 

 When the coral sand beaches are high, the boulders on the platform are 

 usually absent, having been ground up into fragments to form the sand 

 beaches or the coral shingle beaches so characteristic, as we found later, 

 of the outer beaches of the atolls in the Paumotus (PI. 4, fig. 2), and 

 which often run unbroken for miles on the lee side of the atolls. 



The reaches of old reef rock on the outer beaches ai'e mixed with recent 

 stratified beach rock (PI. 8, figs. 1, 11), or with a conglomerate or breccia of 

 corals, consisting of recent coral fragments and of fi'agments or masses of 

 the underlying tertiary coralliferous limestone, so that, unless one has had 

 some experience with the coral rocks composing this heterogeneous mass, it 

 is difficult to make out its composition, and it would be most natui'al to 

 assume that the conglomerate or coral breccia was composed only of frag- 

 ments of recent corals more or less weathered, cemented together, after 

 having been piled up on the underlying tertiary coralliferous reef rock. 



Avatoru Pass (PI. 4, fig. 1) is nearly a quarter of a mile wide and more 

 than half a mile long, with a depth ranging from 15 fathoms at the outer en- 

 trance to three or four fiithoms at tlie bar (PI. 205, fig. 3) on the inner side 

 of the pass, which deepens rapidly to 9 or 10 fathoms towards the interior of 

 the lagoon. The bar is more or less connected with the spit which extends 

 from the southern point of Brander Island (Motoufara). On steaming in we 

 found a strong current of from four and a half to five knots running out of 

 the lagoon. In the pass itself are corals growing in profusion down to 9 or 

 10 fathoms, then thinning out gradually to 20 fathoms. They also grow 

 abundantly on the inner lagoon faces of the islands forming the outer land 

 rim of the atoll, and extend into 5 to 9 fathoms. On the islets which 

 occur in the lagoon (PI. 205, fig. 3), such as Brander (PI. 12, fig. 1) and 

 Mohican Island (PI. 7). corals are found on all the slopes extending 

 into the deeper water of the lagoon from two to three feet to 8 or 9 

 fathoms. The inner extremity of Avatoru Pass is cut in two by Brander 



