26 
level of the overwhelming waters. There is a very general im- 
pression that volcanic action was on a grander scale in past 
geological ages than at present, but there is good reason to believe 
that ‘‘ voleanic energy ”’ is a ‘‘ constant quantity ” and that though 
it changes its scene of action, it does not uwlter or vary in amount 
(Judd). Harthquakes are so rare in England, and so comparatively 
slight, that few of us perhaps quite realise how constant and 
stupendous are these forces, even at the present moment. It has 
been calculated (Huxley) that there are certainly not less than 
three shocks of earthquake a week, and could we obtain records 
daily from the whole surface of the globe, it would be found that 
valcanic action was positively unceasing in one place or another. 
Even in England during the relatively short period of historical 
times, there have been recorded 500 shocks of earthquake, and, 
taking the records of the whole inhabited world, no less than 70,000, 
by means of which many millions of lives have been lost. Earth- 
quakes and volcanoes are generally spoken of as different manifest- 
ations of the same explosive force, but I think there are good 
grounds for believing that, taking into account the cavernous or 
cellular condition of parts of the earth’s crust, caused by the solvent 
action of water, and the enormous cavities created by the evolution 
of carbonic acid gas, there must occasionally be tremendous con- 
vulsions caused by subsidences of the roofs of these vast caverns, 
accompanied by terrific reports from the fracture of rocky beds and 
strata, and that these causes alone would account for many of the 
vibrations and minor earthquakes and earth-tremblings, apart from 
voleanic action. Of course I do not fora moment mean to assert 
that these subsidences would be sufficient to cause the more stupen- 
dous earthquakes felt for great distances, for these are undoubtedly 
of voleanic origin. Ti.ese gigantic throes, the earth waves and 
upheavals, are the result of pent- up forces striving to find an outlet. 
All experience teaches that earthquakes and voleanoes stand in 
inverse ratio one to the other. I mean that the maximum of one 
corresponds to the minimum of the other, so that earthquakes are 
always more violent and numerous immediately before the eruption 
of the nearest volcanic outlet, an outlet, by the way, often situated 
hundreds of miles distant. An earthquake may be appropriately 
described as an earth wave—a billow of solid earth moving, just 
like a wave of the sea, often with a velocity of from 20 to 28 miles 
a minute (Humbolt) and with an undulatory motion such as you 
may see when a heavy carpet is shaken at one end. It has two 
distinct movements, one vertical, i.e, up and down, the other 
horizontal; and it is this second linear movement which is so fatal 
to buildings, for, of course, it operates at right angles to them, 
tending to rend or overthrow them, as shown on this diagram. 
