In a few localities around the Maltese
islands it is possible to find what looks like mounds of reddish-brown soil
with stones and pebbles embedded in it. On close inspection one realises that
what looks like soil is a solid structure as hard as the surrounding rocks.
These geological features were formed after the Maltese islands emerged from
beneath the surface of the sea were they were formed. One can find such
structures among other places at Wied Magħlaq and Pembroke.
The Maltese islands are made up of five
layers of sedimentary rock. The oldest layer started to be deposited thirty to
thirty five million years ago making the Maltese islands relatively young in
geological terms.
The topmost layer, therefore the most recent
layer to be formed is known as upper coralline limestone is usually more 150
metres thick. The second layer which is made up of Greensand is absent from
many areas and which is nowhere thicker than thirteen metres. This is followed
by the blue clay layer underneath which one finds the globigerina limestone
which can be as thin as 20 metres in some places and thicker than 100 in
others. The oldest layer is the lower coralline limestone which is very similar
to the upper coralline limestone and which like it is very thick.
Beneath these five layers are even older layers
which cannot be seen without drilling through the lower coralline limestone.
The
emergence of the Maltese islands above the surface of the sea did not mean the
end of rock formation.
The rocks which formed after the emergence
of the islands from the sea are known as quaternary deposits because they were
formed during the quaternary period. This period started just over two and a half
million years ago. It s defined by a number of ice ages with warm periods in
between. This period is divided into two - the Pleistocene which ended about
twelve thousand years ago and the Holocene, the period in which we are living.
The Holocene is considered as the most recent interglacial warm period.
During the Quaternary sea levels went up
end down depending on the temperature. During Ice Ages evaporated water
precipitated as snow and ice and formed thick glaciers leading to lower sea
levels. In higher temperatures the glaciers melted and sea levels became
higher. The low water level uncovered the sea bottom between Malta , Sicily
and the Italian mainland creating a large continuous landmass. T
he weather was
also characterised by heavy precipitation and the creation of several valleys
which were formed by large amounts of flowing water which carry with them large
quantities of sediment and debris including soil, pebbles rocks as well as
small and large organisms.
The quaternary deposits were carries down
such valleys although it is possible that many of them were formed during the
Holocene period.
This article wsa published in The Times of Malta on 30 October 2014.
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