We live within a rich tapestry of landscapes here in Rideau country. Nature's landforms and farm fields give us perceptions of length and width. But whether it be giant sunflowers in our garden or this cliff near Philipsville, our eyes are drawn to that third dimension within which we live, the dimension of height. Be it the CN Tower built by people or Mt. Everest built by continents in collision, the vertical dimension gives us special fascination. We envy birds that soar through the three dimensions of air. We are awed by whales that glide through the three dimensions of sea. We share genes with chimpanzees that leap through the three dimensions of forest. These layers of beautiful sandstone overlooking the Harts Gravel Road are in real 3D. And this vertical dimension in stone invites us to contemplate that fourth dimension, the dimension of time.
The family of sedimentary rocks is characterized by layers called strata. Strata may be mere centimeters in thickness as you see in the highway cut south of Elgin. In the walls of Zion Canyon in Utah you can see layers of sandstone that are many metres thick. Sandstone strata such as those in this cliff near Philipsville took form in ancient beaches and dunes, probably much like the beaches and dunes you see now at Sandbanks Provincial Park near Picton. Over time, minerals such as calcite and hematite cemented the grains of sand together into sandstone. Rub your fingers across sandstone and you can feel the grittiness of its original sand grains. The layers of limestone you see as you drive along 401 north of Kingston were formed from myriad shells of critters, many microscopic, some bigger. They lived, died and settled like snow to the bottom of a shallow sea that once flooded and ebbed across the Michigan Basin over 400 million years ago. You may remember the lyric "a treat to beat your feet in the Mississippi mud". Over eons of time, river mud may turn into layers of shale as did the Queenston shale beneath Niagara Falls. Eventually, the briny Michigan "Sea" dried out and left massive layers of rock salt beneath Goderich, salt for our winter roads and french fries. Hard pebbles, boulders, sometimes nuggets of gold in ancient river beds have been cemented into layers of sedimentary rock called conglomerate. This you can see as you wonder and wander along the Sandstone Trail at Charleston Lake Provincial Park. Sorry, no gold nuggets there. The remains of giant fern trees and tiny algae were interred in ancient swamps. Over millenia, this organic matter became compressed into the seams of coal as beneath Pictou, Nova Scotia and Wabamum, Alberta. These a few examples of common rocks of the sedimentary family. Wasn't that early geologist, Sherlock Holmes once quoted as saying, "It's sedimentary, my dear Watson"?
But why are sedimentary rocks in layers? Why does one stratum stop forming, then a new layer starts forming on top of it? Maybe a volcano spread a distinctive layer of ash over eons of beach. Maybe a flooding river spewed a thin layer of fine clay over desert sands. Maybe a change in sea currents terminated the formation of one stratum of limestone and triggered a new layer with advanced models of shelled critters that thrived in a new marine environment. A prolonged drought ended the formation of one coal seam. A new flooding nurtured another forest, another seam. The reasons are many.
Each layer of sedimentary rock is like a page in the book of geological time. As you read the chapter of the "Philipsville Cliff", the first and oldest page is at the bottom. The youngest page is at the top. This is the Law of Superposition, a simple and logical law in the geology of sedimentary rocks. Each cliff, each canyon wall, each highway rock cut in sedimentary rock can be read like part of a book. "The Philipsville Cliff" has a few dozen pages. The Niagara Escarpment has hundreds of pages in G-time. The Grand Canyon has thousands of pages, an encyclopedia. Rivers such as the Niagara and the Colorado are like giant saws that cut deep into nature's chronicle of sedimentary rock. Each severed layer of rock gives clues to the environment and life written therein. This is nature's lithography, the original Guttenburg press.
The Philipsville site once was at the coast of a Paleozoic sea which flooded this part of our planet's real estate close to 600 million years ago. In some of its layers you can see cross-bedding as you can see when digging into the Sandbanks near Picton to build a sand castle. Here at Philipsville, layers of ancient sandstone have been quarried to build a church. Now a residence, this Church of the Japanese Martyrs has another amazing tale to tell the history detective. Near Elgin, thicker strata of this sturdy sandstone were quarried and masoned into the Great Horseshoe Dam at Jones Falls and locks from Jones to Newboro. Britain claims the Elgin Marbles. Here in the Keystone of the Rideau, a World Heritage Site, we might rightfully claim the Elgin Sandstone. Many elegant sandstone homes of local farm and village were fashioned of this legacy from a Paleozoic seashore. Strata of this same sandstone quarried near Ottawa provided ashlars for magnificent buildings fitting of our nation's capital. Hence it has been named not Elgin but Nepean Sandstone, basic buff in color with some beautiful red stain by hematite.
Is the Law of Superposition infallible? If layers of sedimentary rock are undisturbed as in this cliff near Philipsville, it is simple logic that the bottom layer will be oldest and the uppermost layer the youngest. But in places like the Rockies, intense mountain-building has occurred. Great sequences of sedimentary rock have been folded, stood on end, faulted, even turned upside down. On the other side of our continent, a giant slab of rock from deep beneath the sea floor has been pushed to the top of the landscape of western Newfoundland. It stands to-day as a barren slab of geology so foreign to our planet's surface that most plants don't know how to live on it. Indeed geology's Law of Superposition is not quite infallible. But were the Laws of Hammurabi infallible? And the Laws of Moses, even though cast in stone?
The story in stone of the Philipsville cliff began over half-a-billion years ago. Fast forward to 10 000 years ago to the end of the Wisconsin Ice Age. Snows of many millennia had been locked in a great Laurentide Ice Sheet and were melting away. A great wall of bluish glacial ice peppered with boulders and clays was retreating northward across Rideau country. For centuries, this damming ice blocked drainage down the lower St. Lawrence Valley. Enormous amounts of meltwater had to find ways southward by channels such as the Hudson Valley. Ancient Beverly Lake and Gananoque River were two of many links in the deluges of many summers. This enormous flow was made even more chaotic by boulder dams left by the melting ice. Further, the weight of an ice sheet had depressed the thin crust of our planet by many metres. This is called isostatic depression and it further contorted drainage. Even now the ground beneath us is slowly rising. Occasionally Granny's fancy chinaware chatters on her shelf due to minor earthquakes of adjustment. The Great Lakes have changed shapes and levels. Hudson Bay is still draining as northern North America slowly inhales a sigh of relief. This is isostatic rebound.
Cold summer winds poured off the retreating ice sheet. A much deeper and higher Beverly Lake was made turbulent during those summers nine millennia ago. Near the top of the Philipsville cliff are notches where waves carved away softer layers of the Nepean sandstone. Harder layers stand out. Downslope, washed and sorted layers of beach gravels covered the sandstone cliff and now give rich rootage for trees. In one place, this shoreline gravel has been dug away for construction material. There you can see how these gravels protected the cliff face from the waves of the receding lake. Across Harts Gravel Road are fertile fields, soils of clays and loams deposited on the floor of a once deeper and more extensive Beverly Lake. Thousands of years after their deposit, these fertile fields nurture a prosperous farm and agri-business.
The third and vertical dimension of the Philipsville cliff leads us into that fourth dimension of time: of minutes for a Brockville rifleman to scale up its face: for a Rideau student to belay down, of thousands of years and Ice Ages past, of half-a-billion years and Paleozoic seas past. We live in space and time. We recollect our past, maybe recess time at Philipsville School or maybe experiences of World War II. We contemplate the future, as immediate as "What's for Supper?" and as abstract as "How will we deal with climate change?" How will we deal with the space and the time that we have? For one and all, that's the challenge as we move and live in our future, our next dimension on our favorite planet.
Geology/Natural History tours are sponsored annually by the Bastard and S. Burgess Heritage Society on the third Sunday afternoon of September (subject to weather) when we look at some of the sites of significance in our local and very rich natural history.