THE MECHANISM OF VOLCANIC ACTION. 
[With 3 plates.] 
By H. J. JOHNSTON-LAVIS, M. D., F. G. S., ete., 
Professor of Vulcanology in the Royal University of Naples. 
In a discussion of this kind it is advisable to be as concise as pos- 
sible, eliminating minor details, so as to give prominence to the main 
outlines of any theory one holds. This communication, which the 
Council of the Ninth International Congress of Geography have hon- 
ored me by asking me to address to you, I propose to put into the 
form of a “credo.” To this I shall add a few fundamental facts 
upon which my reasoning was based, leaving minor ones for discus- 
sion at greater leisure elsewhere. For convenience, I propose to 
divide my theory into two sections. In the first I shall review what 
may be conveniently called deep volcanic action, and in the second, 
that group of phenomena that occur when igneous matter nearly 
reaches the surface or actually finds ap exit thereon. Unfortunately, 
in the first case I am obliged to rely on hypotheses and deductions, 
whereas in the second section, that of superficial volcanic action, there 
are a number of fundamental facts and observations upon which to 
base speculation, and to which I propose to draw your attention. 
Of one fact we are certain, and that is our globe is surrounded by 
a solid crust, which wherever it can be examined shows unmistakable 
and almost universal evidence of compression, wrinkling, and dis- 
location. This crumpling and crushing are equally inexplicable, 
unless we admit that since the initial solidification of the earth’s 
crust its lower, still cooling part or support has undergone contrac- 
tion so as to crowd together the already cooled burden of the upper 
part that this contracting mass carries. 
No one has yet attempted to even suggest that the part of our globe 
subjacent to the solid crust has shrunk from other causes than a loss 
of heat. We may, therefore, look upon the idea of contraction as 
due to cooling to be a universally accepted fact. 
@ Reprinted by permission from The Geological Magazine, London, new series, 
decade v, vol. 6, No. 10, October, 1909. Address to the International Geo- 
graphical Congress. 
305 
