Notes on the Geology of the Tonga Islands

Abstract

I. Introduction. Very little of a detailed character has, so far as I am aware, been published on the geology of the Tonga Islands. Prof. Dana makes a brief mention of some of the islands in ‘Coral and Coral Islands’ ; and in the edition of ‘Coral Reefs’ punished in 1874 Darwin gave a summary of what was known of the group. I spent several months in Tonga in 1889 and 1890, and had opportunit, ies of visiting some of the islands in H.M.S. ‘Egeria,’ which was engaged, for part of the time, in making a survey. Such observations as I made on the geology of the group are embodied in the following notes. II . Topography of the Group. The Tonga or Friendly Islands are situated in the Pacific Ocean between 18° and 22° 309 lat. S., and on either side of the 175th degree long. W. Tongatabu lies a little over 1000 miles to the N.N.E. of Auckland in New Zealand. The large islands of Fiji are about 400 miles to the W.N.W., and those of Samoa about 300 miles to the N.N.E. The greater number of islands fall into three main groups. The northernmost is Vavau, which consists of one moderately large island (about 13 miles in its longest diameter), giving its name to the group, and a number of islets lying to the south and south-west of it. Rather more than fifty miles to the south is the Hapai group, containing the high volcanic islands of