Our first educational series ("Walk and Talk") event took place this past Saturday. Dr. Martin Gibling hosted a hardy crew of interested participants on the chilly beach. Dr. Gibling and his students have long been researching the Site and he is our guest "blogger" for the month of May:
When Sir Charles Lyell visited Joggins in the 1840s, he was stunned
by what he found. He had earlier published his classic text “Principles of Geology”, which was carried
on board the H.M.S. Beagle by the
young Charles Darwin as he embarked in 1831 on his momentous voyage around the
world. Nevertheless, although Lyell was widely regarded as the leading geologist
of his time, he was unprepared for what he found at Joggins. Joggins was the
type historical example par excellence
of the Carboniferous world. Or, in the words of my colleague John Calder,
Joggins was to Charles Lyell what the Galapagos Islands were to Charles Darwin.
What made Joggins so special for Lyell? You have to stand on
the shore at Lower Cove to appreciate how Joggins startled that eminent
Victorian geologist. From Lower Cove, you can look across the tidal waters of
Chignecto Bay to the huge line of cliffs that run for more than a kilometer around
Coalmine Point to Joggins village. If it is a sunny afternoon, you can see the gently
dipping layers of Carboniferous strata lighted up in the cliff face -- nearly a
thousand metres of rock measured bed by bed and representing perhaps a million years
of geological time.
Gazing at the Fossil Cliffs brightened in this way, Lyell must
suddenly have realized that each bed represents the landscape of the
Carboniferous Earth at a moment in time. Originally laid down as soft sand, mud
or peat, the layers were buried as the land subsided, became rock over eons of
time, were tilted by earth movements, and finally were brought back up to the Earth’s
surface, to be etched out by wind and tide to form the Fossil Cliffs.
I can picture Sir Charles tripping over a boulder on the
beach as he gazed at the cliffs, cursing, and simultaneously exulting at his
sudden insight. Why hadn’t he appreciated this before? Each bed surface was a
landscape upon which the rain fell, upon which the fabulous plants of the
Carboniferous era grew, and over which extinct arthropods and tetrapods lumbered.
The Fossil Cliffs were a record of hundreds of such successive landscapes, each
active for a short time and then buried by new sediment and a new landscape.
Few places in the world yielded such a remarkable record.
Today I am walking from Lower Cove towards Joggins. Here in
the cliffs is a thin black layer of coal – formerly a peat, a mass of wetland roots
and plants. On top of the dipping coal seam stands an upright tree trunk, still
preserved where it grew rooted within the peat. Perhaps the bones of the
world’s earliest reptile, Hylonomus, lie
within the once-hollow trunk, as Lyell himself discovered where trees had
fallen from the cliffs.
Here is a former soil, marked by the presence of cracks,
dark organic litter, and the large roots of the lycopsid trees. A forest once
grew on the soil, but only the sediment into which the roots were thrust has
survived.
And here is a river channel – a deep, narrow cut visible in
the cliffs and filled with sand and mud laid down when the river was active.
After a while, the flow must have broken through the banks to gouge out a new
course, leaving this reach abandoned. On the beach below the river layers, a
block bears the trackway of a gigantic arthropleurid – perhaps the largest arthropod
ever to have existed. The creature must have wandered down into the abandoned
channel to search for drifted leaves or stranded logs.
Perhaps it is imagination or just wishful thinking, but I find
that I can actively turn the layer into a landscape in my mind without much effort.
I see the groves of horsetails and the huge lycopsid trees moving in the wind.
There is an arthropleurid proceeding between the trunks, its multiple legs
moving in waves on either side, oblivious of my presence. And do I hear flowing
water as the river makes its way to the sea?
Approaching Coalmine Point, I halt in amazement. There, high
in the cliff, is the edge of a former river channel, and on its bank stand two
upright lycopsid trees, the broken-off trunks still more than a metre high and
tilted towards the channel. The trees seem to be conspirators of the forest
community, whispering together of life in the landscapes of the Carboniferous.
-Dr. Martin Gibling, Dalhousie University
.tif)
Posts
