W. M. Davis — Shaler Memorial Study of Coral Beefs. 255 



begun anew, after most of the total submergence was accom- 

 plished. 



The Mevated Loyalty Atolls. — The three Loyalty islands, 

 between New Caledonia and the New Hebrides, are elevated 

 atolls. The two southeastern members, Lifu and Mare, are 

 plateau-like masses, about 50 and 40 kil. in diameter; their 

 margins are a little higher than their broad central plain, 

 which is in both islands remarkably level over large areas at 

 an altitude of about 40 meters in Lifu and 70 in Mare. Their 

 external slopes are very little dissected ; hence their emergence 

 must be of recent date. A French observer, Balanza, has 

 reported that fossil corals are abundant in the higher margin 

 of Lifu, but that the limestone of the central plain shows no 

 stratification and contains only fossil shells. This is incon- 

 sistent with the theory of an outgrowing reef on a still-stand- 

 ing foundation, back of which the lagoon is excavated by 

 solution ; for the lagoon floor of such a reef should show a 

 slanting stratification and contain abundant fragments of coral ; 

 but it is consistent with the theory of an upgrowing reef on a 

 subsiding foundation, for the lagoon deposits of such a reef are 

 largely free from corals. Mare is of special interest from pos- 

 sessing in its center a low knob of dense volcanic rock, a few 

 hundred meters in diameter, some ten meters in relief, with 

 gentle lateral slopes ; hence not so high as the plateau margin. 

 The limestone close around the knob shows no signs of altera- 

 tion or disturbance by intrusion. This is interpreted to mean 

 that the knob is the top of a subsiding volcanic island, from 

 which the loose-textured, scoriaceous surface parts had been 

 denuded so far as to give the highest summit a well-subdued 

 form before submergence allowed the deposition of the lagoon 

 limestone around it. The knob cannot owe its reduction in 

 size to wave attack on a still-standing island ; for, in that case, 

 it should still be bordered by cliffs, while as a matter of fact, 

 its slopes are very gentle ; absence of dissection on the outer 

 slopes of the island shows that emergence is of too late a date 

 for any sea cliffs, a little earlier cut by the waves in hard vol- 

 canic rocks, to have disappeared since then by weathering. 

 Nor can the knob owe its reduction in size to the general 

 degradation of a still-standing island, for in that case much 

 volcanic detritus should be found over the limestone plateau, 

 yet no trace of such detritus is to be seen. A boring in the 

 limestone a kilometer distant from the knob might be expected 

 to reach volcanic rock at a depth of some 200 meters ; the mix- 

 ture of volcanic detritus with limestone in increasing propor- 

 tion as the volcanic rock is approached, would be decisive in 

 favor of submergence during the upgrowth of the reef. If the 

 buried slopes of the denuded volcano are similar to those of 



Am. Jour. Sci. — Fourth Series, Vol. XL, No. 237. — September, 1915. 

 17 



