Feet
At Chiloe the recent elevation has been 350
„ Concepcion „ „ 625 to 1,000
„ Valparaiso „ „ 1,300
„ Coquimbo „ „ 252
„ Lima „ „ 85
Shells, similar to those clinging to uplifted rocks, which are
evidences of these elevations, still exist in the neighbouring seas,
and in the same proportionate numbers as they are found in the upraised
beds. In addition to this, Mr. Darwin shows us that at Lima, during the
Indo-human period, the elevation has been at least eighty-five feet.
At Valparaiso, during the last 220 years, the rise was about nineteen
feet, and in the seventeen years subsequent to 1817 the rise has been
ten or eleven feet, a portion only of which can be attributed to
earthquakes. In 1834 the rise there was apparently still in progress.
At Chiloe there has been a gradual elevation of about four feet in four
years. These, together with numerous other examples, testify to the
gradual but, as compared with other parts of the globe, exceedingly
rapid rise of the ground upon the western shores of South America.[158]
The most important point to be noticed is that this district of rapid
elevation is one of the most earthquake-shaken regions of the world.
And further, judging from Darwin’s remarks, in those portions of it
where the movements have been the most extensive, and at the same time
probably the most rapid, the seismic disturbances appear to have been
the most noticeable.
Similar remarks may be applied to Japan, it being in those districts
where evidences of recent elevation are abundant that earthquakes
are numerous. Thus, in the bay of Yedo, where we have borings of
lithodomi in the tufaceous cliffs ten feet above high-water mark,
which, inasmuch as the rock in which they are found is soft and easily
weathered, indicate an exceedingly rapid elevation, earthquakes are of
common occurrence.
From the evidences of elevation which we have upon the South American
coast, Japan, and in other countries, it appears that these movements
are intermittent, there being periods of rest, when sea cliffs are
denuded, and perhaps even periods of subsidence. There is also evidence
to show that, although these movements have been gradual from time to
time, they have been aided by starts occasioned by earthquakes.
As to whether earthquakes are more numerous during periods of
elevation, or of subsidence, or during the intermediate periods of
rest, we have no evidence.
Sudden displacements which occasionally accompany earthquakes might, it
was said, sometimes be regarded as the _cause_ of an earthquake, and
sometimes as the _effect_.
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