CAUSE OF EARTHQUAKES—HOBBS 269 
and successions by a bent wire, it was necessary to employ three com- 
plicated snarls of wire in order to cover a minute only of time. Such 
a result favors strongly the view that not one fault slip but very many 
on differently placed surfaces are the cause of the earthquake 
phenomena.”* 
GENERAL STATEMENT OF PROBABLE CAUSE OF EARTHQUAKES 
Proximate cause.—The proximate cause, or in common language 
the occasion, of earthquakes, so far as they occur within the earth- 
quake girdles of the earth, would seem to be the formation of a fold 
or flexure within near-surface earth strata; such flexure being inci- 
dent to the erection of a range of growing mountains of scalloped 
pattern accompanied by a series of parallel deep troughs. Such ele- 
vation of a mountain range is accompanied as a natural consequence 
by pockets of lava beneath the arch, and above these are formed a 
series of vents for the escape of the volcanic materials, both molten 
rock and gases. 
If we omit the special characteristics, the proximate cause of 
earthquakes may be stated to be adjustments which take place in 
position or inclination of portions of the outer shell of the earth, and 
this broad general statement may be applied outside as well as inside 
the earth’s earthquake girdles. Such adjustment on the basis of many 
observations implies many individual movements among blocks com- 
posing a fault mosaic. 
Ultimate cause—The ultimate cause of earthquakes, the deep- 
seated reason for the changes brought about in the configuration of 
the earth’s surface, is by geologists generally believed to be the con- 
tinuous loss into surrounding space of the heat from the earth’s in- 
terior portions. This loss of heat is accompanied by a reduction of 
volume, a shrinking of the interior core of the earth; and the outer 
shell of rock being already cooled to a relatively stable condition 
must wrinkle as it adjusts itself. The old illustration of an apple 
in late winter which wrinkles from the loss of water and consequent 
reduction of volume of its interior portion, may still serve well at 
the present time. 
PART II—EARTHQUAKES OF THE EASTERN UNITED STATES 
THE REGION A RELATIVELY STABLE ONE 
Historical earthquakes of the region.—Northeastern North Amer- 
ica lies outside the seismic girdles of the earth (see fig. 2, p. 265) 
and at least since its settlement by Europeans it has relatively seldom 
been vexed by destructive earthquakes. That light shocks have not 
1. Sekiya, “A model to show the motion of an earth particle during an earthquake,” 
Trans. Seis. Soc. Japan, vol. 11, 1887, pp. 175-177, pls. 1-2. 
