ilO ART. 3. — B. kOTÛ : 



describes a large ring, the edge of which is signaHzed by a series 

 of fumes well seen from a distance. It is the remarkable example 

 of a ring of loet fumaroles around the central arena where dry 

 hot invisible ones exist which prevent the precipitation by the high 

 tension of rising vapor. After rainy weather the fumaroles in- 

 crease considerably in intensity^' — a fact which speaks for the 

 atmospheric origin of the vapor. The arena of this amphitheater 

 was formed by the settling"^ of cooled crust in the unsupported 

 subterranean channel which was made vacant probably through the 

 escape underneath of uncooled magma outwards, and which was 

 unable to bear the superincumbent w^eight of the crust. 



Lav a -deltas are by no means rare when fluent lava crawls 

 down into the sea ; but what the writer finds particularly remark- 

 able is the wdde circular depression, or ' foundered ' arena, as in 

 Fig. 3, PI. XII., the formation of which must have caused many 

 lava-tunnels in making way for the exit of fl.uent lava into the 

 surrounding sea-bottom. 



Y. The Temperature of Lavas. — On the intratelluric temperature 

 of the magma within the upper portion of the crust we have only 

 scanty data on which to make even an approximate estimation. 

 There seems, however, not much difference between the initial 

 temperature^^ at the vent and in the channel below 6-8 km. from 

 the surface within the compression shell, as may be deduced 



1) See page 116. See also PI. IX. Fig. 1. 



2) Pyrogenous settlings «ire teclmically called ' foimclering ' by Daly and other Americau 

 writers. 



3) J. P. Iddings also says, that the temperature of the earth's interior is not greater than 

 the hottest volcanic lava, that is to say, it ranges from 1,000° to 1,5()0°C. The soiirce of the 

 hottest volcanic magma, according to this authority and to J. Milne, is located at a dejîth of 30 

 miles (48 km.), which is the base of the lithosphère at the boundary of the crystalhne and 

 amorphous zones, and the upper limit of the magma region, according to F. v. Wolff, is 

 30-40 km. Iddings, ' The Problem of Volcanism,' 1915, p. 156 (d scq. "Wolff, ' Dor Vulkanismus,' 

 1914, Bd. I. S. 31. 



