The rocks here are part of the Geo Centre’s “Great Rock Wall”. Its story begins 550 million years ago (mya) when turbulent currents scoured broad scoop-shaped channels in layers of sand and salt. After they hardened in beds of rock, powerful tectonic forces tilted them and then extensive fractures developed. Millions of years of weathering and erosion along major fracture planes, resulted in exposure of an enormous rock wall. Glaciers polished the steeply southward inclined surface. After the glaciers retreated, a small pond formed within the narrow depression, adjacent to the rock face. Overtime, a bog filled in the pond and the great wall was preserved.
Over 550 mya, this area was part of large complex, seaside delta plain, perhaps as large as the present Mississippi Delta. Meandering rivers and floods that carried and deposited sediment from the eroded mountain range from north. Eventually, thick layers accumulated on the plain, in front of the delta extending it to the sea. Some rocks near here contain fossils of marine plankton and thin layers of volcanic ash, which tell of intermittent volcanic eruptions.
Channels are fundamental features of today’s rivers, deltas, estuaries, and marine environments. Knowledge of helps us understand the origins of ancient channels to be seen in the rocks of Signal Hill today. Rivers flowing over the plains, first scour and then occupy their channels. As rivers meander from place to place from their channels, they fill in the old channels with sand and new channels are formed. In modern environments, thin beds of sand, silt, and mud are commonly associated with thick channel sands, sometimes laid down beyond the channels during flooding or high water periods.
Between 15,000 and 11,000 years ago, the climate began to warm and glaciers covering the Avalon Peninsula and Grand Banks began to melt and retreat. Gradually, the rocks high on Signal Hill began to merge. A rocky, barren and frigid landscape slowly appeared. About 11,000 years ago, retreating glaciers of the Northeastern Avalon Peninsula deposited large quantities of meltwater, which contributed to innumerable ponds and streams. Evidence of climate change and vegetation, from the time of up to present were found in core samples of pollen and plant were preserved in organic mud deposited at the bottoms of ponds. Pollen studies by Memorial University researchers with radiocarbon dating and research by the Geological Survey of Canada show immediately glaciers melted, climate was cold and most of the vegetation in the northeast Avalon was mostly tundra. The climate warmed to a maximum in the period of 8,000 and 4,000 years before present. With warming, tundra gave way to low shrubs followed by the boreal forest which contain spruce, balsam fir, and birch. During the past 4,000 years, there has been overall climate cooling, with frequent cold and warm cycles. Our climate gradually changes.
Interesting links:
http://www.nr.gov.nl.ca/mines&en/publications/geology/report90-2.pdf/
http://www.geocentre.ca/
http://www.heritage.nf.ca/environment/mine/ch4p6.html