ON THE FACTS AND THEORY OF EARTHQUAKE PHENOMENA. 67 
80 little is yet known beyond the general fact that northwards the seismic 
bands appear to follow the great river-courses, or more probably the great 
axes bounding ¢hem,—and passing also the so frequently convulsed Chinese 
empire, which appears to have two chief seismic centres about Pekin and 
Canton (these cities have been the centres of observation for all, or nearly all, 
the Chinese records of earthquakes that we possess, and hence one reason of 
the depth of seismic tint around them; but it is also to be observed that two 
of the great volcanic districts of the “ Fire Hills and Fire Wells” of China are 
situated within the tinted or shaken regions adjacent to the two capitals), 
with a third more central volcanic region, of which I am not aware that any- 
thing is known seismically,—and remarking the apparent exemption of Cochin 
China, for which there are no records,—we at length arrive at the greatest and 
most formidable earthquake- and volcanic region upon our globe. Stretching 
in a vast horse-shoe, convex to the south, from Burmah and Pegu, and sur- 
rounding the great island of Borrieo, with an intervening belt of sea, and 
reaching round to Formosa on the north-west, we have an almost continuous 
girdle of volcanoes and lofty mountains. Every island of the group, in- 
cluding Java and Sumatra, Celebes and Mindanao, is shaken with earth- 
quakes the most formidable and frequent ; and we can point to no spots upon 
the whole earth’s surface upon which seismic energy is exhibited with an 
intensity equal to that of Luzon and Sumbava. 
Nothing even in South America or Mexico appears to rival the grandeur 
of volcanic energy and resultant seismic action here. In 1815 the thunder- 
ings of Tomboro, in Sumbava, were heard nearly 1000 miles away (through 
the earth no doubt). The ashes, or, more correctly, the finely-divided tufa- 
dust, floating in the air, made mid-day into darkness 300 miles away in Java, 
and were precipitated at sea even a thousand miles from the point of ejec- 
tion, while whole tracts of country, with inhabited towns, have suddenly 
become engulphed and disappeared during periods of eruption, which over 
a large portion of the chain, from one extreme to the other, are almost 
continuous. 
It will be remarked that the seismic tint is both more intense and rela- 
tively more circumscribed in area along the bands that surround the linear 
voleanic vents, where they cluster thick, than along mountain-chains or 
ridges that. possess few or no volcanic vents. This no doubt arises from the 
centres of impulse in active volcanic lines being situated at a comparatively 
small depth, in fact, coming from the actual bases of the crater, or not far 
beneath ; and hence the horizontal propagation is not so great for a given 
force of impulse as where its centre is situated deeper, and the explosive 
effort rendered abortive to rupture the solid crust above. The intensity of 
tint in the former case is due to repetition of effort, as well as to occasional 
intensity of impulse. 
An earthquake in a non-volcanic region may, in fact, be viewed as an 
uncompleted effort to establish a volcano. The forees of explosion and 
impulse are the same in both; they differ only in degree of energy, or in the 
Varying sorts and degrees of resistance opposed to them. ‘There is more 
than a mere vaguely admitted connexion between them, as heretofore com- 
monly acknowledged—one so vague, that the earthquake has been often 
Stated to be the cause of the volcano (Johnston, ‘ Phys. Atlas,’ Geology, 
p-21), and more commonly the volcano the cause of the earthquake, neither 
View being the expression of the truth of nature. They are not in the rela- 
tion to each other of cause and effect, but are both unequal manifestations 
of a common force under different conditions. 
Further north we have the somewhat less terrible, but yet deeply- 
FZ 
