OF THK TONGA ISLANDS. 591 



the group, and a number of islets lying to the south and south-wost 

 of it. lliither more than fifty miles to tlie south is the TTapai 

 group, containing the higli volcanic islands of Tofua and Kao on the 

 west ; on the east a chain of low, fiat, coral islets ; the Kotu group 

 in the centre ; and on the south a number of isolated islands, the 

 largest of which is j^omuka. Some fifty miles to the soutli and 

 somewhat to the west of Nomuka lies Tongatabu, the largest island 

 of the group, measuring over twenty miles in its longest diameter, 

 A channel about ten miles broad separates Tongatabu from the 

 small and high islaud of Eua to the south-east, while eighty-five 

 miles to the south-west lies the little island called Ata by the 

 natives, the Pylstaart of the charts, the most southerly outlier 

 of the Tonga Islands. (See Map on p. 594 and PL XXIII.) 



Lying far to the north of the islands mentioned arc jS'iuafou 

 (=Good Hope, or Proby Island), Keppel, and Boscawen Islands, 

 which, though politically belonging to Tonga, occupy an inter- 

 mediate-position between this group, Fiji, and Samoa. 



III. Geological Characteks op the Group. 



According to the characters which they present, the Tonga 

 Islands may be arranged in three divisions, viz. : — (a) purely 

 volcanic islands ; (6) islands formed of volcanic materials laid out 

 beneath the sea, and since elevated, with or without a covering of 

 reef-limestones ; and (c) islands formed entirely of reef-limestones. 



(a) The Volcanic Islands. 



The purely volcanic islands form a line running parallel to the 

 long axis of the group, but a little to the west of it. The direction 

 of this line is approximately JN'.N.E. and S.S.AV. 



At the southern end is the little island of Ata or Pylstaart, 

 which, judging from the extremely steep and rugged outline that 

 it presents, may possibly be a member of this series. I have, 

 however, merely seen a pliotograph of the island, and it can therefore 

 only provisionally be reckoned a member of the volcanic series. 



The islands of Honga-tonga and Honga-hapai, lying north of 

 the west end of Tongatabu, are I believe the fragments of an old 

 crater. They stand out of the sea about a mile and a half apart, 

 and reach a height of some 300 and 200 feet respectively. Each 

 island has a high vertical face on the side turned towards the 

 other, and on all sides hard black layers of rock are seen alternating 

 with softer ones, and slope away from a point situated between the 

 two islands. 



Fifteen miles to the north of these islands is the recently-formed 

 volcanic mound named F'alcon Island. 



In the year 1S(57, H.M.S. ' Falcon ' reported a shoal in the position 

 <>f the present island, and ten years later smoke was seen issuing 

 from the sea at this spot by H.M.S. ' Sap])ho.' In October 1885, a 

 submarine volcano suddenly burst into activity, and built up a 



