'")00 MR. J. J. LISTER ON THE GEOLOGY 



35. Notes on the Geology of the Tonga Islands. By J. J. Lister, 

 Esq., M.A. (Head June 24, 1891.) 



[Communicated by J. E. Marr, Esq., M.A., F.R.S., Sec. G.S.] 



[Plate XXIII.J 



Contents. 



Page 



I. Introduction 590 



II. TopoGUAPiiY OP the Group 590 



III. Geological Ciiasacters op the Group. 



(a) The Volcaniclslands 591 



{h) Islands formed of Sedimentary Volcanic 



Material 595 



(c) Islands formed entirely of Limestone 606 



IV. CoxcLusroN 616 



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 ' 

 published in 1874 Darwin gave a summary of what was known of 

 the group t. 



I spent several months in Tonga in 1889 and 1890, and had 

 opportunities 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. 



I am indebted to Mr. Alfred Harker, M.A., E.G.S., who has 

 examined the volcanic rocks which I obtained J, and also to Dr. 

 John Murra}^ who has looked over sections of the calcareous rocks 

 of Eua. 



II. Topography or the Group. 



The Tonga or Friendly Islands are situated in the Pacific Ocean 

 between 18° and 22° 30' lat. S., and on either side of the IToth 

 degree long. W. Tongatabu lies a little over 1000 miles to the 

 N.F.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 Yavau, which consists of one moderately large 

 island (about 13 miles in its longest diameter), giving its name to 



* 2nd ed., pp. 288 & 289. 

 t P. 212 and elsewhere, 3rd ed. (1889). 



J Mr. Harker has published notes on these specimens in the Geol. Mag. 

 for June, 1891. 



