368 Revieivs — Agassi&'s Coral Reefs of the Pacific. 



a well-developed land-rim on the weather-face flanked on the lee 

 by submerged reef-flats. 



Finally, such islands and islets as Tikei, Nukutavake, and a 

 number of small islands with central sinks and depressions formed 

 by the beaches thrown up on the outer edge of the flat or summit 

 of the island, leaving an open central space enclosed by the beach- 

 dams. Similar islands occur in the Gilbert group, as Arorai and 

 Tamaua ; Mejit, Lib, and Jemo in the Marshall and Nurakita, and 

 Nanomana in the Ellice groups." (p. xxviii.) 



The Ellice group is of especial interest to geologists in this 

 country, as it was in the island atoll of Funafuti, one of this group, 

 that the Royal Society decided to make trial borings to ascertain its 

 structure, and Professor Sollas^ commenced work on 21st May, 1896, 

 a task which was continued by the Government of New South 

 Wales,^ under the direction of Professor Edgeworth David, F.E.S. 

 After various trial borings, a boring 947 feet, or 147 feet below the 

 base of the steepest cliff, was accomplished, the material passed 

 through being coral limestone, containing numerous well-preserved 

 corals. 



Professor Agassiz has evidently felt the importance of this 

 investigation, for he has devoted seventeen pages to a description 

 of this atoll, and three plates and three charts to its illustration. 



" All the soundings known indicate that coral reefs rise 

 independently upon summits formed by Tertiary limestones or 

 volcanic rocks, summits which have been formed either by elevation 

 or submarine denudation, or upon summits of accretion forming 

 submarine banks. 



"The nature of the underlying base is naturally an important 

 factor in determining the pitch of the sea slope ; we may assume 

 that the steep slopes of the upper part of reefs is due to the 

 sloughing off of the limestone cliffs down to thirty or forty fathoms, 

 much as they are sloughed off from the faces of elevated islands 

 above high-water mark. If composed of volcanic ash or harder 

 volcanic materials the slope in one case will be very slight, 

 spreading rapidly laterally under the influence of the waves ; in 

 the other, the slope of volcanic material will not differ materially 

 under water from that above high- water mark. When the slope 

 is a talus of reef material it may lie at a steep angle or may follow 

 closely the slope of the underlying base below the depth at which 

 corals or NuUipores grow." (p. xxx.) 



It had been Professor Agassiz' intention, he tells us, to investigate 

 the marine fauna of each of the great oceanic groups of islands 

 and trace the passage of the littoral into the abyssal fauna, and 

 to obtain the material needed for a comparison of isolated oceanic 

 faunae to one another. Unfortunately he was unable to carry out 

 this part of the programme. 



It is refreshing to find the author expressing the opinion, that in 



1 Proc. Eoy. Soc, 1897, pp. 602-515. 



2 Natural Science, 1899, pp. 17-37 ; and Proc. Eoy. Soc, December, 1897, 

 pp. 200-202. 



