292 STUDIES FOR STUDENTS 
there is independence of the seismicity and volcanicity . . . . There is coincidence 
between the unstable regions and eruptions. ... . But one phenomenon does 
not in a marked degree cause the other. This last negative law, which clearly 
results from the statistical researches, requires, however, a more detailed study. 
From all this we may conclude that, in general, earthquakes are a phenomenon 
purely geological, and that quite certainly they have their origin in dynamic 
causes by the effect of which the actual relief of the land is produced and of which 
they are the ultimate manifestation. 
This conclusion of de Montessus is in harmony with that of Milne, 
who by an analysis of 10,000 earthquake observations in Japan 
showed that there were comparatively few which had their origin 
near to the volcanoes of the country. 
As regards the broad distribution of the unstable areas upon the 
globe a most important law is discovered: 
The earth’s crust quakes in nearly equal amount and in a unique manner 
along two narrow zones which are disposed on two great circles (in the geometrical 
sense of the word), which include between them an angle of about 67 degrees—the 
Mediterranean-Alps-Caucasus-Himalaya circle (53.54 per cent. of the shocks) and 
the circumpacific or Andes-Japan-Malay circle (41.05 per cent. of the shocks). 
These two zones coincide with the two most important lines of relief of the terrestrial 
SUMPOCE Memien ee. The zones including the seismic regions coincide exactly with 
the geosynclinals of the secondary era, as they have been charted by Haug in his 
well-known work, Les géosinclinaux et les aires continentales. The geosynclinals 
(the most mobile zones of the earth’s surface) where the sediments have been deposited 
in greatest thicknesses, have been energetically folded, dislocated, and re-elevated in 
the Tertiary period at the time of the formation of the principal actual ranges (or 
geoanticlinals); and include in themselves, with two or three doubtful exceptions, 
all the seismic regions (in the sense which we have given to these two words) 
which, in consequence, characterize them. 
Fig. 1, which has been reproduced with additional data from de 
Montessus’ maps, indicates the position of the geosynclinals between 
the continental areas, and in black the seismic areas. De Montessus’ 
latest work, from which these plates and the above extracts have 
been taken, has recently issued from the press. This work is devoted 
to the study of the geological structure of the unstable regions of the 
globe, and follows as a natural sequel to the completed catalogue of 
seisms by the same author. ‘The soul of the work, as he frankly 
admits, is to be found in the generalizations of Bertrand, de Lapparant, 
t F, de Montessus de Ballore, Les tremblements de terre: Géographie séismologique; 
with a preface by M. A de Lapparant (Paris, 1906). 
