Here we see rocks in the field, in natural outcrops, in man-made
quarries or the stonemason's yard. Rocks are infinitely diverse,
becoming even more so the closer one looks. Geologists have
brought as much order in this diversity as possible, starting with
a subdivision in three major categories: igneous, sedimentary
and metamorphic rocks.
'Igneous rocks' could be considered as the primary rocks on
earth, formed by the solidification of magma in the deeper
reaches of the earth's crust or of lava that has ascended to the
surface. Examples of igneous rock are granite, dolerite, basalt
and rhyolite.
'Sedimentary rocks' are those deposited in oceans, lakes,
deserts, or other parts of the earth's surface by the activities of
water, wind, ice, or chemical precipitation. Sedimentary rocks
are usually bedded, layer-by-Iayer, and capable of reaching massive thickness. A few examples are shale, sandstone, limestone
and rock-salt.
'Metamorphic rocks' are igneous or sedimentary rocks that
have been altered into a totally different rock by high pressure
and temperature, as well as by chemical processes. This happens
after such rocks have been buried at appreciable depth below
the earth's surface. Limestone, for example, is altered into marble, sandstone into quartzite, claystone and shale into slate or
schist, etc.
All these rock types can be further subdivided into a highly differentiated array, each with their own characteristics, each
telling their own story of times long past. Geology is ever so
creative!
THE GIA S CAUSEWAY These columnar basalts along
the Antrim coast of Northern Ireland are part of a large series
of extrusive rocks, straddling the Northern Channel and reappearing along the western Scottish coast, where a renowned
outcrop is Fingal's Cave on the Isle of Staffa. Legend has it that
the Irish giant, Finn Mac Cool, created the Causeway as a suite of
steppingstones for an invasion of Scotland.The Causeway is only
one of many examples that exist all over the world, of a striking
outcrop or rock being the subject of superstition and ancient
myths.
C
TA
Late afternoon sunlight falls on the
majestic basalt columns in a quarry in the German Eiffel region,
where such columns are still actively exploited for various applications in construction.
ROCK
24
COLUM
R
S TSoftly curved basalt columns and
smoothly rounded boulders create a deceptive air of stillness
and kindliness near Framnes, on the North Icelandic coast.
Like an indestructible totem pole, hewn from granite,
this rock stands watch on the stormy ocean coast ofTorndirrup,
near Albany in southern Australia.
PARTITION The drama of erosion is well exhibited in this
scene in the Petrified Forest Park, Arizona, USA. Long ago, a
huge chunk of sandstone parted from its massive, maternal formation to start a life of it's own. After being worn and rounded
by wind and water, that very chunk falls apart by the same forces
and weaknesses by which it originally came loose.
BEEFY BE CH This assembly of pebbles, interspersed on a
bedrock of beefy-red jasper, along the seashore of Point Samson,
West Australia, is derived from some of the oldest dateable formations on earth.Their age is in the range of 3 billion years!
Granite and gneiss make up large
stretches of the southwestern coast of Australia, like here at
Cape Leeuwin on the very southwestern tip of the continent.
These rocks are gorgeously sculpted and molded by the pounding waves of the Indian Ocean. Standing here, staring out, one
may see a ship or the occasional whale, but beyond that there is
nothing, nothing but ocean for thousands of miles, until the
chaste and chilly whiteness ofAntarctica dooms up.
T E R 0 SOURCE Iron gives an arresting red tint to a
travertine deposit precipitated from a small spring in Kirkjufell, a
volcanic region in southern Iceland. The snow has just barely
melted, as can be told from the bleached green of the grass
fringing the spring.
I U
Granite is usually thought of as a
rather forbidding rock, massive and grey. But that is not always
true. Here, in Ploumanach, in northern Brittany, France, the sea
and other elements have played about with this crude and austere rock, sculpting it into gracious, if not lascivious forms.
hese menacing jaws only seemingly disrupt the serene
harmony of the famed, bone-white travertine deposits of
Pamukkale,Turkey.
quarries or the stonemason's yard. Rocks are infinitely diverse,
becoming even more so the closer one looks. Geologists have
brought as much order in this diversity as possible, starting with
a subdivision in three major categories: igneous, sedimentary
and metamorphic rocks.
'Igneous rocks' could be considered as the primary rocks on
earth, formed by the solidification of magma in the deeper
reaches of the earth's crust or of lava that has ascended to the
surface. Examples of igneous rock are granite, dolerite, basalt
and rhyolite.
'Sedimentary rocks' are those deposited in oceans, lakes,
deserts, or other parts of the earth's surface by the activities of
water, wind, ice, or chemical precipitation. Sedimentary rocks
are usually bedded, layer-by-Iayer, and capable of reaching massive thickness. A few examples are shale, sandstone, limestone
and rock-salt.
'Metamorphic rocks' are igneous or sedimentary rocks that
have been altered into a totally different rock by high pressure
and temperature, as well as by chemical processes. This happens
after such rocks have been buried at appreciable depth below
the earth's surface. Limestone, for example, is altered into marble, sandstone into quartzite, claystone and shale into slate or
schist, etc.
All these rock types can be further subdivided into a highly differentiated array, each with their own characteristics, each
telling their own story of times long past. Geology is ever so
creative!
THE GIA S CAUSEWAY These columnar basalts along
the Antrim coast of Northern Ireland are part of a large series
of extrusive rocks, straddling the Northern Channel and reappearing along the western Scottish coast, where a renowned
outcrop is Fingal's Cave on the Isle of Staffa. Legend has it that
the Irish giant, Finn Mac Cool, created the Causeway as a suite of
steppingstones for an invasion of Scotland.The Causeway is only
one of many examples that exist all over the world, of a striking
outcrop or rock being the subject of superstition and ancient
myths.
C
TA
Late afternoon sunlight falls on the
majestic basalt columns in a quarry in the German Eiffel region,
where such columns are still actively exploited for various applications in construction.
ROCK
24
COLUM
R
S TSoftly curved basalt columns and
smoothly rounded boulders create a deceptive air of stillness
and kindliness near Framnes, on the North Icelandic coast.
Like an indestructible totem pole, hewn from granite,
this rock stands watch on the stormy ocean coast ofTorndirrup,
near Albany in southern Australia.
PARTITION The drama of erosion is well exhibited in this
scene in the Petrified Forest Park, Arizona, USA. Long ago, a
huge chunk of sandstone parted from its massive, maternal formation to start a life of it's own. After being worn and rounded
by wind and water, that very chunk falls apart by the same forces
and weaknesses by which it originally came loose.
BEEFY BE CH This assembly of pebbles, interspersed on a
bedrock of beefy-red jasper, along the seashore of Point Samson,
West Australia, is derived from some of the oldest dateable formations on earth.Their age is in the range of 3 billion years!
Granite and gneiss make up large
stretches of the southwestern coast of Australia, like here at
Cape Leeuwin on the very southwestern tip of the continent.
These rocks are gorgeously sculpted and molded by the pounding waves of the Indian Ocean. Standing here, staring out, one
may see a ship or the occasional whale, but beyond that there is
nothing, nothing but ocean for thousands of miles, until the
chaste and chilly whiteness ofAntarctica dooms up.
T E R 0 SOURCE Iron gives an arresting red tint to a
travertine deposit precipitated from a small spring in Kirkjufell, a
volcanic region in southern Iceland. The snow has just barely
melted, as can be told from the bleached green of the grass
fringing the spring.
I U
Granite is usually thought of as a
rather forbidding rock, massive and grey. But that is not always
true. Here, in Ploumanach, in northern Brittany, France, the sea
and other elements have played about with this crude and austere rock, sculpting it into gracious, if not lascivious forms.
hese menacing jaws only seemingly disrupt the serene
harmony of the famed, bone-white travertine deposits of
Pamukkale,Turkey.