Los Angeles herald., 1907-02-03
QUEER ISLAND OF JAMAICA
Grobou of Columbia University in View


dence continued the island became
more contracted again, and fringing
coral reefs began to form on its sub
merged borders. These coral reefs are
now above water level, proving that
the latest movement in this region has
been an upward one for the land, and
corresponding Increase In the size
of the island
The reader has now surveyed in out
line the history Of Jamaica from the
time when its present site was CEN
ter Of volcanic activity perhaps FIVE or
six millions of years ago. to the pres
ent He has seen great mountain sys-
tens forming, by a violent crumpling
of enormous masses OF strata, and he
has seen these mountains disappear
again, through erosion and subsistence,
until I'm their stead reigned the still
ness of the central sea" Great upward
and great downward movements, whose
amplitude Is measured I'm thousands of
feet characterized this earlier period,
and that these oscillations of the rocky
crust of the earth were accompanied
by violent seismic disturbances can
scarcely be questioned. Other UP and
down movements succeeded, but these
were of less amplitude.
Like the dying oscillations of the PEN
dulum, each later swing fell short OF
the preceding one; each succeeding elc-
walton or depression was of less magni-
tude than it's predecessor. With the de.
creasing magnitude of terrestrial oscil-
lation the decrease in the violence Of
seismic disturbance probably goes hand
in hand. Therefore, as Jamaica gradu-
ally acquires stability, we may .con-
fidently hold that 1t is less and less
likely that earthquakes or other great
disturbances should visit the island.
a Fault" the Cause
But, it will be asked, what is the i'm
mediate cause of the earthquake just
reported from this region?" The only
answer that can be given at present is
that probably the usual cause of earth
tremors was operative here that Is,
there occurred a slight readjustment of
the rocks of the island or of the neigh
boring submerged area, a break in the
strata, and a slipping of one side over
the other, producing what biologists
call fault. Such breaks and accom-
panying earthquakes must have been
numerous in the earlier history of this
region, but are probably decreasing in
frequency and violence. Accordingly
the present disturbance, violent though
1t may appear, and disastrous in It's
effects, so far as man is concerned, is,
after ALL only one of the dying shud-
ders of a Mechanically and seismically
old region. And yet who is to say that
regeneration may not take place In
some future age? A new period of
mountain making and of volcanic and
other disturbances may be inauguratel,
and new mountains come into existence
where now are stumps of the mountains
of the past. At present, however there
is no indication that such a renewal of
wont n f11lDaSS iS in
Deformation of Earth's Crust
1t should be clearly understood that
there is no volcanic activity on the
island at the present time. There have
been no surface eruptions since late
Cretacic time, or approximately for the
last 100000 years. There were some
intrusions of volcanic lavas into the
rocky crust from a deeper horizon, but
these intrusions never reached the sur
face. But folding and bending of the
strata of the earth's crust occurred III
the Jamaican region in much more re-
cent times, and this, so far as the evil .
dence goes, is the cause of the earth
quakes, and not volcanic activity. The
rending of the strata, however, has
steadily decreased in amount to the
present time until for some ages past
1t has been manifest only as a process
of warping, or slight rending, affecting
wide areas. Locally, this is shown by a
relative rise or fall of the sea level, but
1t is primarily the result of deforma-
tion of the earth's crust. Such deforma-
ton is accompanied by breaking and
slipping of strata, and this becomes
manifest on the surface as an earth
quake shock.