1920.] Jaggar.—New Zealand Volcano Research. 165 
“ dermolith ” is smooth lava with a membrane or skin outside,, and 
spherical vesicles ; “ clastolith” is scoriaceous lava with deformed vesicles ; 
“ perilith ” is the confining wall of a live lava-system, whether it bound 
fissures, or a crater, or a complex of both. 
The Hawaiian Observatory, where the seismographs are mounted, is 
twenty-two miles nearly east of the high central crater of Mauna Loa. 
This crater is considered the main volcanic centrum for the Hawaiian 
volcanic system. A zone of rifts passes through this crater, different parts 
of which have emitted lava at different times, and it is the distance of 
this zone from the observatory which is spoken of in the following as 
“ Mauna Loa distance.” Kilauea Mountain, where the observatory is 
placed, has other fault-fractures and lava-vents not so far away, and these 
are referred to in the mention of “ shorter distance.” 
Summary of Results. 
Lava-column. 
1. The hypomagma, with reagent gases in solution, dominantly hydrogen, 
carbon compounds, and sulphur, is the actuating medium for the phenomena 
of volcanism. 
2. The pyromagma, vesiculated and heated by gases, is the fluent lava 
of volcanoes described as dermolithic—the pahoelioe of Hawaii. Gases 
escape from solution within it and react exothermally up to the time of 
•congelation. 
3. The epimagma is made by subaerial processes, where convectional 
stirring or flowage releases gas completely, and the vesiculate residue 
solidifies in granular or efflorescent forms. These are described as clas- 
tolithic lava—the aa of Hawaii. 
4. The bench magma of Halemaumau, the mobile floors, crags, and lake- 
bottoms of the lava-pools, is epimagma mixed with congealed pyromagma. 
5. The effective structural unit in active volcanicity is the volcanic 
system, a rift complex ; and the lava-column is bounded by the perilith, 
the confining wall of the volcanic system. 
6. The lava-column is a foam bubbling more or less as gases are released 
by change of pressure, and more or less viscous as heated by gas reactions. 
Pressure may be increased and gas-release restrained by its own dermal 
■consolidation. 
7. Oxidation of the iron through invasion of epimagma tic vesicles by 
air, while clastolithic lava is hot, is apparent in such lava, and may be 
a powerful exothermic agency in keeping such lava fluid. 
8. There is a complicated crateral circulation maintained by convection : 
effervescing pyromagma rises, and both its crusts and its epimagmatic 
residue sink ; pyromagma maintains a tubular plexus in the mobile sub¬ 
stance of the bench magma ; this substance is itself in slow circulation 
under the weighting of overflows and the accretions of epimagma. The 
hypomagma beneath is sensitive to the pressure-effects. There is an 
incessant deep flow of the under-substances towards the region of minimum 
load. 
9. Tumefaction in hypomagma is propagated in the directions of least 
loading wherever bubble-pressure gains headway and releases new gas to 
the bubble form. Linear expansion in the perilith by gas heating may 
contribute to the surface evidence of tumescence. 
Seismic Effects. 
10. Underground magma is restrained by the perilith. Trigger-release 
of pressure resides in the seasonal tides that pass through the rock crust 
