﻿Vol. 66.~] VOLCANO OF MATAVANU IN SAVAII. 639 



Plate LI. 



An explosion as the lava falls into the sea. — This photograph, 

 for permission to reproduce which I have to thank Capt. Allen, was taken by 

 him from the cooled and solidified surface of the lava, near the spot where the 

 still liquid mass from beneath was running into the sea, not far from the site 

 of Toapaipai. Masses of red hot lava are seen in the air, each leaving a track 

 of steam behind it. I saw many such explosions through the binocular, but 

 did not get near enough to obtain a photograph equal to this. 



Plate LII. 



Lava in the lagoon, near Saleaula. — The lava in the background 

 above high-water mark has cooled slowly, and had time to assume the usual 

 corded structm-e. In the foreground, between tide-Limits, many of the lobes 

 have flowed into the water and been chilled before they had time to do this. 

 They present a structure resembling one variety of pillow-lava. 



[Note. — The dates of the various lava-flows stated on p. 624 were taken in 

 1909 from Amtmann Williams's notes. The map on p. 622, with his latest 

 corrections, was not received until the text was in type. The few small discre- 

 pancies will not, it is hoped, materially affect the general narrative.] 



Discussion. 



Sir Aechibald Geikxe commented on the interesting character 

 of the discourse to which they had listened, and on the instructive 

 pictures which, as shown on the screen, had brought the details of 

 a little-known volcanic region so vividly before their eyes. The type 

 of volcanic action described by the Author belonged to that which 

 had long been familiar as displayed by the Hawaiian volcanoes, 

 but a special value attached to his observations on the end of the 

 lava-stream where it enters the sea. The speaker believed that 

 never before had the phenomena there presented been so closely 

 watched and so instructively photographed. The Author de- 

 served infinite credit for the courage and persistence which, in 

 spite of a trying temporary lameness, had overcome all tne natural 

 difficulties of the place, and had enabled him to bring home so large 

 an amount of material for the elucidation of various problems in 

 the mechanism of volcanoes. 



Mr. H. H. Thomas, referring to the motion of fluid lava beneath a 

 solid crust, mentioned an area of 200 square miles of lava in Central 

 Iceland, which was covered with subsidiary vents or spiracles rising 

 to heights of 10 or 15 feet above the average surface. 



The President (Prof. Watts) said that he was much impressed 

 by the Author's description of the origin of pillow-lava. It had 

 long been thought that this structure was the result of basic lava 

 pouring into the sea, but this appeared to be the first case in 

 which the actual production of it had been observed and described. 



The Author, in reply, said that the spiracles mentioned by 

 Mr. Thomas were very abundant in the Myvatn district of Iceland, 

 and were generally, and he believed correctly, attributed to the 

 hot lava flowing over mud or similar wet material. The steam 

 generated made its way up through the lava, escaped through 

 cracks in the crust, and blew out masses of pasty lava which fell 

 round the orifice and built up the cones referred to. 



