Prince Edward County, Ontario, Canada
O U R N A T U R A L H E R I T A G E
UNDER THE SOIL THERE IS A LOT OF ROCK
Thursday, May 28, 2009
From the high bluffs of Point Traverse, under almost any kind of viewing conditions, you can look across the wide expanse of Prince Edward Bay and see it. It breaks the distant landscape of North Marysburgh, standing out like a buffy smudge on an otherwise regular shoreline. It is the unmistakable landmark called Cape Vesey, known by many of the locals, as simply, The Rock. And a rock it is for sure, some 100 feet in height, ending almost as inexplicably as it begins.
To understand its presence, we have to go back a few years – well, at least 950 million years ago anyway, if we want to start at the beginning, the Precambrian period, when the land was relatively flat and featureless. There was granite rock, and we can see this of course in the Canadian Shield, where spectacular Precambrian rock is evident for all to view. We have it here in Prince Edward County too, but it is some 300 metres or 1,000 feet below the surface, and that is a long way down indeed.
In the next era, the Palaeozoic, the county was alternately buried beneath the sea and then lifted above it. During each sea invasion, sediments were deposited on the ocean floor, gradually hardening to form the typical sedimentary rock types such as limestone and shale, something County residents can now relate to and bringing us more up to date. We’re talking only 12,000 years ago now, the period known as the Great Ice Age, when erosion predominated. It was during this time when limestone rock walled valleys and high cliffs such as The Rock were formed.
Other spectacular formations were left behind too, such as McMahon Bluff, at Black River. This high mountainous feature is known as a mesa, an expression we seldom hear in these parts, as the term is more applicable to southwestern United States, where the Spanish name means flat topped mountains. In the Guayana highlands of South America, these same table top mountains are called tepuis. Angel Falls, the highest waterfall in the world, drops from one such tepui.
Here in Prince Edward County though, we seem to go from one extreme to the other. From the high rocky formations at Cape Vesey and McMahon Bluff, to a flat island of rock at Scotch Bonnet, spectacular in its own right since the island is several layers of flat limestone rock, barely rising above the level of Lake Ontario. The only soil is a sparse patch near the remains of the old limestone lighthouse where a cluster of shrubs gave up their fight for survival several years ago. Although an island, the limestone shelves are really nothing more than a shoal that has risen above the level of Lake Ontario, one of many such limestone shelves extending far out into the lake from similar shelves along the Huyck’s Point shoreline.
However, the most spectacular rock formation of all is the Ameliasburgh Inlier, along Victoria Road, just west of Highway 62. At over 950 million years of age, this granite knob decided long ago for reasons best known to itself, to become a rare phenomenon, the southernmost extension of the Canadian Shield in this part of Ontario. It is only 13 acres in size, but identical in every way to its counterparts north of Highway 7. Plants such as pale corydalis, marginal shield fern and rock polypody grow here, plants more at home in the Canadian Shield. Further investigation might even reveal sweet fern, a species of bayberry also common in the northern regions of the province.
We take these unusual rock formations for granted as we see them every day in our travels. Many questions relating to how they evolved remain hidden though, and they do not give up their secrets easily. All we can do is speculate as to the turn of events, resulting in their formation, knowing that each episode in Prince Edward County’s geological history influenced the landscape we see today as part of our natural heritage.
This is the seventh in a series of columns by Terry Sprague on the natural heritage of Prince Edward County, sponsored by the Prince Edward Stewardship Council. For more information, check out their website at http://www.ontariostewardship.org .