BY H. I. JENSEN. 665 



of their age and history, and of the volcanoes which have 

 produced them. I have shown that the Samoan islands lie on a 

 fissure running W.N.W.-E.S.W., almost at right angles to the 

 great fissure running from Samoa to New Zealand. It is 

 probably on account of the situation of these islands on the inter- 

 section of two great structural lines, that volcanic extravasation 

 has been so great here. The elevation of coral reefs and atolls in 

 the Tongan group has been shown to be probably due to a great 

 earth-folding and continent-making movement tending to restore 

 the old continent of Fiji; and most likely a continuation of the 

 movement that raised New Zealand in late Tertiary times, 

 leaving Miocene and Pliocene limestones high and dry. Structu- 

 rally the two regions are alike. A glance at the geological map 

 of New Zealand, and the Admiralty map of the Tongan group, 

 will serve to show that, just as the east of New Zealand is 

 composed mainly of- Tertiary sediments overlying older meta- 

 morphic and plutonic rocks; and the west coast is mostly covered 

 with Tertiary eruptive rocks, and has a sharp faulted front 

 towards the deep ocean; so Tonga has her raised limestones to 

 the eastward of the line of volcanic activity, and a fault and 

 downthrow behind, that is to the west of this line. I have 

 suggested that the folding has come from the west. Owing to 

 the magnitude and length of the fault it is most likely to be 

 normal, and in the rear of the anticline. 



I have tried to show that the phenomena observed at the 

 Savaiian volcano afford us some clue to the direction in which 

 to look for future developments in preparing forecasts of earth- 

 quakes and eruptions. 



The eruption has been shown to be due to a movement along 

 the great structural line between Samoa and New Zealand which 

 opened the fissure in 1902; the increase of folding, consequent 

 upon the rise of the isogeotherms accompanying the sunspot max- 

 imum of 1905, caused the remelting of magmas at a depth, and 

 squeezed them into the fissure, whence they have been escaping 

 from several vents. The ingress of sea-water has had something 



