John P. Greenhouse
As sightseeing companions geologists can be irritating. Instead of basking in the majesty of, say, a Grand Canyon or a Kilimanjaro they can spoil your trip by worrying about how it was formed, why it’s where it is and not 20 km to the east or west, and so on. Take the Elora Gorge. Why should it shatter the gentle, rolling valley of the Grand River just as it passes through our area? Why is the gorge at Elora and not Inverhaugh, or Belwood? Why does the river flow through Elora and not, say, Alma? Where did it flow 20,000 years ago, before the most recent glaciers reshaped our landscape? Could there be other gorges beneath the sands, gravels and clays that blanket our part of Ontario?
Hillock Farms on Nichol Concession 1 (Figure 1 - right) just south of Water Street (South River Road) decided they needed more water for their pigs. Last fall they hired a drilling contractor who began drilling near the barn, about 100 metres southeast of the existing well which had entered bedrock at 20 metres. To his surprise, the contractor drilled almost 70 metres without encountering the bedrock. Not only was the bedrock much deeper than he expected, but he had to drill through sloppy, quicksand-like materials for much of the way. The well eventually penetrated the bedrock and produced water from a fracture, but it was very expensive for the contractor.
Sometimes, basic scientific curiosity and the problems of everyday life can relate to each other, and this is a case in point. Geoscientists at UW and elsewhere have to several years wondered about the origins and history of the Elora Gorge and about the nature of earlier versions of this important drainage system for south central Ontario. They have many questions, and some answers.
"Other" gorge is a 20,00-year-old landmark
The drilling contractor at Hillock Farms, like others before him over the past half century, has inadvertently discovered one of those answers for himself by drilling into the "other" Elora Gorge. Although completely filled in today, this other ancient canyon was a landmark 20,000 years ago that would make our present tourist attraction pale by comparison. If early Ontario-man had a Mill Street, it would certainly have been on Nichol Township Rd. 6, about 400 metres southeast of the intersection with Nichol Concession Rd. 1. It would have overlooked a canyon twice as deep as our today. It may even have attracted honeymooners!
Today's landscape is still very new
To understand this it helps to go back a bit. The Grand River today drains south central Ontario to Lake Erie, its route determined by the vagaries of the topography that the water encounters on its relentless movement to the south. The Elora Gorge was formed because there is a sharp drop in elevation of the dolomite bedrock in this area that causes the river to move faster and therefore erode more quickly.
The landscape of today, however, is from a geological point of view at least – very new. A series of ice advances over the past several hundred thousand years has, like a fleet of bulldozers, continually resculpted the overburden deposits (loose materials, sands, gravels, and clays) over the bedrock surface. It is thought that we are presently in a warm spell between ice advances that has lasted 12,000 years. The present river has established itself over this lull. But 35,000 years or so ago, the world was enjoying a similar warm interlude and another river almost certainly drained ancient south central Ontario towards an ancient Lake Erie. That river, encountering the bedrock slope near Elora, would presumably also have eroded its way down into the dolomite bedrock as our river is doing today. For this reason, we should not be surprised to find one or more ancient gorges in our area, buried beneath the rubble of the glacial advances that followed that earlier (geologically) brief period in the sun.
Well drillers helped verify gorge's existence
The ancient gorge intersected by the contractor at Hillock Farms is known formally as the Elora-Fergus Buried Valley. It was officially discovered in the late sixties by Dr. Paul Karrow of the University of Waterloo as he pain-stakingly put together the reports on unusually deep bedrock provided to the Ontario Ministry of the Environment by local water well drillers. It is the local drillers, therefore, who should take much of the credit. Omer Gow and John Cudney are said to have been the first to report one of these bedrock "holes" while drilling at the Beatty Experimental Farm near Fergus in the 1930’s. Expecting to find dolomite bedrock at 5 to 10 metres, they ended up drilling 60 metres through overburden before abandoning the hole. Not only was the overburden thick, but it had the consistency of a quicksand and they had to use drill sleeves to support the walls. Periodically thereafter, other wells would reach unexpectedly large depths without encountering bedrock. Bob Gow, Omer’s son and also a driller, recognized in the late ‘50s that these "holes" could be connected on a map to form a river-valley-like feature running across the area more or less parallel to the present Grand River. More details have been provided by UW geophysics students Yuhiko Arai, Kian Jensen, Paul Lee and Stephen Hilton who have located the ancient valley with seismic and gravimeter surveys.
The result of all this work is summarized in Figure 1 on which the location of the ancient valley is marked by 29 large black dots connected by a black line. Each dot represents a known location of the structure, determined either geophysically or from drilling. (Two crossings, numbers 15 and 28, are not shown on the map as they lie very close to other dots.) The connecting lines are simply a guess as to the path between. The ancient valley joins the present Grand River valley at Belwood Lake (dot 1), crosses it again between Fergus and Elora (14), and crosses or joins it yet again at Inverhaugh (31). In between, the old river wandered across the countryside in a manner reminiscent of the present river, but following a different path.
Figure 2 takes cross-sections of two familiar landmarks, the present Elora Gorge near the Highway 7 bridge and the Niagara River near the Whirlpool Gorge, and compares them with the ancient gorge at a point (17) where it crosses Nichol Township Rd. 6 just south of Hillock Farms. The ancient gorge here is 50 metres deep and about 200 metres wide, as deep as Niagara but much narrower. What a chasm it must have been!
Figure 3 shows a cross-section along the river from Belwood Lake to Inverhaugh. The upper line represents ground level, and the lower line is the estimated elevation of the bedrock on the valley axis. The middle line shows the approximate elevation of the bedrock on either side of the ancient gorge.
You can clearly see the presence of the ancient valley in one place. Where the present Grand River crosses the old gorge behind the Grand River Park subdivision on Bon Accord St., just south of Fergus (between 13 and 14 on the map), the rock walls are missing for a distance of one hundred metres or more. At one point on the south bank you can imagine seeing the sharp edge of the old gorge where the rock wall is abruptly terminated. There are other surface signs. The soft materials filling the old valley are more compressible than the bedrock and depressions overlying the valley axis on roughly 18 of our 31 crossings. At least two of these depressions contain swamps. The Canada Wire and Cable Company on Gartshore Street north of Fergus is built over the valley (between 7 and 8), and there are (unconfirmed) reports of subsidence problems during building.
Old gorge might be a future water source
Drilled into by accident, the Elora-Fergus Buried Valley can be expensive. Like Hillock Farms, the original owners of the Fairview Golf Club had the misfortune many years ago to drill into the ancient gorge (at 2 on the map) for its water supply. They spent a lot more on that well than they expected. If you think that your property is near the old gorge and are considering drilling, you should write to me for a detailed description of each of the crossings shown on the large map. These have been accurately located with respect to a nearby road intersection or other landmark.
Someday, however, we may want to drill water wells into this ancient gorge. At Hillock Farms, as with many of the wells drilled into the valley’s base, a layer of cobble and gravel was found just overlying the bedrock. These gravels are what you would expect to lie at the bottom of a river. They are typically 2 to 3 metres thick and extremely permeable, with the potential to be a very good aquifer. In a test at the crossing of the ancient gorge and Highway 7, the Ontario Ministry of Environment is said to have pumped 200 gallons per minute from this layer. An attempt to complete the well within this layer at Hillock Farms was abandoned because a lot of fine sand was emerging from the aquifer with the water, clogging screens and pumps. This problem can perhaps be overcome with the right drilling technology. Finally, the ancient valley probably the source of rumours that circulate from time to time concerning the existence of vast underground lakes beneath the Fergus-Elora Region, boundless reservoirs which can be tapped to supply the entire regions of Wellington and Waterloo. The old gorge is not a cave filled with water; the groundwater can exist only in the pore spaces within the sands, gravels and clays that now fill it. Still, the other Elora Gorge may indeed be a water supply of some consequence in the future. It is important that we be aware of its existence, protect it from contamination, and understand its origins and history.
Bibliography
- Arai, Y., 1975. Geophysical investigations of a buried valley south of Belwood Lake, Ontario. BSc Thesis, Department of Earth Sciences, the University of Waterloo, 63p.
- Hilton, S.W., 1978. The Elora-Fergus buried valley: further geophysical studies, MSc Thesis, Department of Earth Sciences, The University of Waterloo.
- Jensen, K.A., 1975. A geophysical investigation for buried valleys in the Belwood Lake area. BSc Thesis, Department of Earth Sciences, The University of Waterloo, 106p.
- Karrow, P.F., 1968. Pleistocene geology of the Guelph area, Ontario. Department of Mines Geological Report #61.
- Lee, Paul F.Y., 1975. Geophysical studies of a buried bedrock channel in the Elora-Fergus region of southwestern Ontario. MSc Thesis, Department of Earth Sciences, The University of Waterloo, 73p.