24(5 
ON THE RECENT RIVIERA EARTHQUAKE. 
uniform, the resulting disturbances consist of an irregular 
series of interrupted starts and jumps, as the successive weak 
points give way under the severe lateral pressure, causing the 
disturbances of the earth’s surface that are felt as earthquakes. 
These vary greatly in intensity from the slight tremours that 
have been felt occasionally in tin's country, seldom sufficient 
to do serious damage, to the fearfully destructive earthquakes 
of other places in which whole towns have been suddenly 
destroyed; there appear to be certain permanent lines of 
weakness in the earth’s crust, such as the west coast of South 
America, where these occurrences are much more frequent 
and more severe than elsewhere. 
It has been inferred from careful examinations of the 
various directions of the forces exhibited in earthquakes, 
that these forces radiate from centres of action at moderate 
depths below the surface, extending probably to not more 
than thirty miles depth at the greatest, and often but little 
exceeding the actual inequalities upon the earth’s surface, 
namely, five miles the height of the highest mountains, and 
five miles the depth of the deepest seas, making ten miles 
total variation in level of the surface of the earth. The 
earthquake phenomena may consequently be looked upon as 
really occurring in the superficial portion of the crust of the 
earth, to a depth probably only two or three times greater than 
the present inequalities upon the surface ; and although the 
damage caused by them to life and property is occasionally 
very severe in amount, it may be questioned whether the 
annual loss from this cause is really any greater on the aver¬ 
age than that arising from storms and floods, the other 
destructive causes that are in continued action on the earth’s 
surface. 
It may be added as an experience of actual beneficial 
effects from an earthquake that has recently occurred in 
North America, where a series of violent earthquake shocks 
have just taken place in Arizona and Mexico, and at twenty 
miles distance from Tucson, in Arizona, that a crater has 
been formed on a mountain, from which streams of water 
have burst forth, redeeming a vast area of country that 
was previously unwatered and sterile; also in the same 
vicinity large tracts of the Santa Catalina mountains 
were torn asunder, revealing rich veins of gold, that 
were previously unknown. The same earthquake was also 
felt at Guaymas, on the coast of Mexico, but there, unfortu¬ 
nately, great damage was done to the buildings and many 
lives were lost. 
