AGASSIZ: FIJI ISLANDS AND CORAL KEEFS. 77 



outer edge upon which corals may flourish and spread seaward, when 

 the talus has reached the depth at which corals can grow. I am iu- 

 clined to think that the examination of such a reef will alone give us 

 an idea of the way in which such thick masses of coralliferous lime- 

 stones were formed, — most pi-obably by a combination of subsidence, 

 of accretion, and of lateral expansion. 



What the exact age of the elevated limestones is, I am as yd unable 

 to state. Their aspect and position show them to be of considoi-able 

 age, and probably antecedent to the present period, and in many ways 

 they resemble some of the late tertiary elevated limestones I have found 

 on the north coast of Cuba. The great thickness which the elevated 

 coralliferous limestones attain in this group, at least 800 feet, also 

 shows that it may have been deposited" during a period of subsidence, 

 but not a period of subsidence in our epoch, or which could have had 

 any effect in shaping the outline of the islands of the Fiji and their 

 accompanying reefs. 



Whether the elevation of the Fiji group corresponds in time with that 

 of the northern part of Queensland, I am unable to state. I can only 

 suggest that it is not improbable that the elevation of Queensland and 

 of the islands to the east of the Solomon, New Hebrides, etc., including 

 the Fijis and Samoa, may have been synchronous, and that these islands 

 have, like uoi'thern Queensland, been subject to an immense denudation 

 and erosion, reducing them to their present proportions. The elevation 

 having probably, as in northern Australia, been preceded in still earlier 

 geological times by a great depression, during which the thick beds of 

 coralliferous limestone may have been formed. Judging from some pho- 

 tographs I have seen, I should feel inclined to consider the atolls of the 

 Paumotus to have been formed by causes similar to those which have 

 shaped those of the Fijis. 



The Tonga Islands as described by Lister^ are arranged by him in 

 three divisions : (a) purely volcanic islands ; (b) islands formed of 

 volcanic materials laid out beneath the sea and since elevated, with or 

 without a covering of reef limestones ; and (e) islands formed entirely of 

 reef limestones. 



The islands of tlie Vavau group consist entirely of limestone, the. for- 

 mation of Avliich must have been at least 300 feet thick. The islands are 

 flat-topped, and the majority stand at one of three levels of elevation. 

 Lister 2 figures the terraces of the islands to the south of Vavau. At 



1 Notes on the Geology of the Tonga Islands. By J. J. Lister. Q. J. Geol. 

 Soc. of London, Vol. XLVIL p. 590, 189L 



2 Loc cit., p. 608. 



