Earthquakes in Nicaragua. — Crawford. 117 
large masses of hard strata ; there was felt a perceptible increase 
and decrease of the oscillations ; then, for about 32 seconds were 
experienced more rapid or vibratory movements of short, high 
waves as if two large masses of rock had (at an interval of about 
15 seconds) suddenly sepai'ated from their places and fallen to 
the hard floor of a cavern, from a hight sufficient to cause a 
slight jar, each 90 miles distant, and converting the energy into 
elastic, longitudinally vibrating^ progressive, spherical waves of 
force. 
No place has been discovered where permanent subsidence of 
the earth's surface has resulted. 
This earthquake was not caused by volcanic forces such as the 
superior energy of high tension gases or aqueous vapors disar- 
ranging earth strata. 
The aqueous vapors arising from the cones of the nearly ex- 
hausted volcanoes on the line of force [Santa Clara, Momotomba, 
and Omatepa] have not increased nor diminished in apparent 
quantity. 
No perceptible change has been observed in the amount or the 
temperature of large springs of water, issuing from fissures, near 
the base of some of the volcanic cones, on the line of force, in 
Nicaragua. 
The primary cause of this class of seismic disturbances in the 
earth's crust in this region can be discussed hereafter when all 
the phenomena referable to this series have been studied. At 
present two theories — each with some good evidence — are pre- 
sented: Firsts — Motion from the interior friction of ''the bodily 
tides" [Prof. Gr. Darwin, Philo. Transt. 1879, parts i, ii,] incident 
to the increased length of the siderial da}' and, probable, conse- 
quent elongation of the earth's polar radius and increased pres- 
sure in equatorial latitudes. Second, — Contraction from secular 
cooling and the consequent increased tension in the narrow strip 
of land, between the line of volcanic masses in Nicaragua and 
the Pacific ocean, acquiring sufficient force to overcome the co- 
hesion and disconnect large masses of strata and precipitate them 
into adjoining caverns deeply located beneath the volcanic cones 
and masses of ejecta. This "sufficient force" appears to have 
attained its maximum annually, or, at intervals of 10 to 14 
months during the past four years, as observed by the writer, in 
