By: Ed Freeman, Toronto
Nature's final shaping of the Greater Toronto Area (GTA) landscape, before being clothed in vegetation, was accomplished by the movement of Halton ice out of the Lake Ontario basin and by the waters of Lake Iroquois. The last icy covering of the Toronto area was during the Port Huron Stage of 13,000 years ago, when a lobe of ice surged into the Lake Ontario basin from the northeast and southwards into New York State and the Niagara Peninsula, and northwestwards and westerly in the Trenton to Hamilton area. This ice deposited Halton Till and molded surface deposits into drumlins. As the ice melted back into the St. Lawrence Valley, its meltwaters filled the Lake Ontario basin until they found an exit past Rome, New York and out the Mohawk and Hudson Valleys to the ocean. This proglacial lake of 12,000 years ago is called Lake Iroquois. During its few hundred years of existence, it eroded a shorebluff averaging 15 m high across the city.
Today this shorebluff slopes from about 53 m above Lake Ontario in the western GTA to 62 m in the eastern GTA and to 138 m at Kingston. This slope reflects the rebounding of the Earth's crust from the weight of glaciation. Since more ice existed and stayed longer in the northeast, the land there is rebounding faster than lands to the southwest. Currently the Thousand Islands area is rebounding about 37 cm per century relative to sea level. This uplift is raising Kingston 17 cm per century more than Toronto and continues to increase the slope of Lake Iroquois's shoreline. The shorebluff and the large masses of sand and gravel deposited as baymouth bars and beach deposits are distinctive features within the GTA. Below the Iroquois shorebluff clays blanket the flat expanse of the former lake bottom, part of which underlies downtown Toronto. Let's travel along some of the city's streets and see the results of this sculpting.
0.0 km Exit Don Valley Brick Works Park left onto Bayview Extension.
0.7 Proceed past Pottery Road exit to Todmorden Mills Museum. Continue up the side of the Don Valley - to your right just before the road bridge over the railway track is a former large landfill site.
1.7 Traffic lights at Nesbitt Drive. Continue up the former ravine of Cudmore Creek that cut through the Lake Iroquois shorebluff and right through the Loblaws parking lot.
2.2 Right on Moore Ave. Right on Mallory Crescent (2.3 km) park at parkette (2.6 km) and walk to edge of Iroquois shorebluff.
The material underfoot is Halton Till deposited by ice flowing to the northwest from out of the Lake Ontario basin. The steep wave cut bluff of Lake Iroquios lies immediately in front and down to the railway tracks that utilize the well drained beach of Lake Iroquois for their roadbed. Imagine Lake Iroquois waters extending out as far as you can see from the gravelly beach on which the railway tracks lie. This shorebluff extends next to the railway tracks from Laird Drive to the east, westward to the Davenport Road underpass just north of Dupont St. At this point the railway swings gradually away from the shorebluff, which then forms the hillside just north of Davenport Road until Caledonia Park Rd.
Continue on Mallory Crescent until Moore Ave. From this point until we descend the Lake Iroquois shorebluff again, the landscape consists of a series of low ridges and drumlins oriented northwest-southeast parallel to the Halton ice flow. Turn left onto Moore Ave. At (4.0 km) dip down into the former valley of Mud Creek and the site where the 1892-1894 Belt Line Railway crossed through into Mt. Pleasant Cemetery.
4.4 Right onto Mt. Pleasant Rd. and continue to Eglinton Ave. 6.1 Left onto Eglinton Av. and rise up onto one of the northwest trending ridges (the ridge top is at Dunfield Av.) and proceed downhill until the valley bottom of the former Taddle Creek at Edith Dr./Colin Av. that flowed along the edge of Eglinton Park (a former brickyard)
7.6 Right onto Avenue Road and up over a drumlin. Turn left at traffic light (8.1 km) onto Roselawn Av. and pause at the radio transmission tower on the top of the drumlin.
8.3 Left onto Castle Knock Rd. and left again onto Kelway Blvd.
8.6 Right onto Avenue Rd. and over the edge of the drumlin, across Eglinton Av. and downhill to the former valley of Yellow Creek (Rosedale Brook) located at the left turn onto Hgy. 11A (Oxton Ave.)
10.0 Right onto Oriole Pky. And up onto a hill upon which Upper Canada College is situated. Swing south onto Avenue Road and continue to
11.7 Edmund Av. on the right at the top of the Lake Iroquois shorebluff. Continue down the shorebluff (called Gallows Hill at one time when a tree bridged the roadcut) to the traffic light at Dupont St.
12.4 Right onto Dupont St. and cross the former Castle Frank Creek at the low spot just before Davenport Rd.
12.8 Right onto Davenport Rd. go under railway bridge and turn left (follow Casa Loma, Davenport signs). The Lake Iroquois shorebluff lies immediately on your right.
13.4 At Spadina Rd.
If you can find a parking spot nearby stop and climb the stairs up the Lake Iroquois shorebluff to get an idea of just how steep and high this wave eroded shorebluff is. While standing on the top of this old shoreline visualize what this area looked like 12,000 years ago. Davenport Rd. and beyond was submerged beneath Lake Iroquois water. Along the beach coarser sand and gravel was left while finer silt and clay settled further south to form a more or less flat sloping lowland, called the Iroqouis Plain upon which Toronto was founded and grew. The steep shorebluff of Lake Iroquois made it difficult to get into or out of the city by overland trails in the early 1800s. Notice that Spadina Rd. just ends at the shoreline. The early north-south streets that crossed this shoreline were developed up ravines where creeks cut through the shorebluff (like Bathurst St.). Historically Native peoples travelled along the base of the shorebluff from the Don River valley to the Humber River passageway to the north, a path now widened into Davenport Rd.
14.0 Cross Bathurst St. Park and view parkette on the corner.
Here you can view the shorebluff and read a plaque about this site.
16.1 At Dufferin St. a good view to the right of the shorebluff and of the Lake Iroquois Plain to the south.
17.0 At Caledonia Park Rd. Here the Lake Iroquois shoreline swung north along the edge of Earlscourt Park to Hgy. 401 as it skirted around the flooded Humber River valley. However erosion along the Lake Iroquois shorebluff deposited a large baymouth bar into the Humber Valley, just as erosion of the Scarborough Bluffs by Lake Ontario deposited the Toronto Islands and created Toronto harbour. Continue on Davenport Rd. and along the top of the old baymouth bar.
17.9 Carleton Village School on the right.
18.0 Right onto Old Weston Rd. then left onto St. Clair Ave. (18.2 km). A number of clay brick yards existed north of St. Clair Ave. in the deeper waters behind the baymouth bar. From Keele St. (18.4 km) the baymouth bar was leveled for supplies of sand and gravel and to build the stock yards, meat packing plants, and railway trackage that used to exist here.
20.8 T-intersection at Scarlett Rd. Turn left under bridge and immediately right onto Dundas St.
21.3 Cross the Humber River.
23.5 Montgomery's Tavern on left just before Islington Av. Continue on Dundas St. to
34.6 Hurontario St. (Hgy. 10). Cross Mary Fix Creek and climb up onto the top of the Lake Iroquois shorebluff again. The bluff is easily seen on the left from Mason Heights Dr. (36.4 km) to Mavis Rd. (36.7 km).
40.0 Cross the Credit River and turn left onto Mississauga Rd. (40.2 km) and immediately left into parkette or park off road to right. Be careful entering or crossing Mississauga Rd.
is on the southeast side of the Credit River bend at Dundas Street and Mississauga Road. The hill capped by cemented gravel is an Iroquois baymouth bar that formed across the flooded Credit River valley. The structures within the concrete channel are energy dissipaters to reduce erosion as storm floods from relatively recently built subdivisions surge into the Credit River. Carefully exit left onto Mississauga Rd. and proceed to
44.8 QEW interchange and return to Toronto. Cross the Credit River bridge (45.3 km) and take the Gardiner Expwy. (58.8 km).
68.3 Exit right at Jarvis St. exit. All the land beneath and to the right from the CNE grounds to the Don River is landfill dumped into Lake Ontario.
69.9 Turn left onto Parliament St. and take first right onto Mill St. past the redevelopment of the former Gooder-ham and Worts distillery site to the end, and
70.9 Left onto Overend St. right (71.1) onto Front St. and north on the Bay-view Extension. This area is known as the West Don Lands (former Ataratiri lands) 32 hectares expropriated by the province for a mixed residential /commercial development for 12,000 to 14,000 persons. Its polluted soils and floodplain location has stalled development.
71.6 Beginning of fill for 'Toronto Viaduct' - fill raised railway lines 4 m across the lakefront to allow vehicular traffic to pass underneath eliminating level crossings.
72.2 Queen Street bridge. The site of the GTR and CPR Don Station now relocated to Todmorden Mills Museum grounds. This was the beginning of the Belt Line Railway that looped northwest to Eglinton Avenue and back down the Humber Valley. Today the Don River is confined to an excavated channel. The presence of its former meandering course can be seen in the infilled meander bends of Riverdale Park West (73.2) and Riverdale Park East (73.4).
Rosedale Valley Road occupies the ravine of Castle Frank Creek (now confined to an underground sewer). Castle Frank - the summer home of Lt. Governor Simcoe (built in 1795, burned down in 1820s) overlooked the valley from a site at the top of the north side of this ravine.
74.1 Across the Don River on the east side lies Chester Springs Marsh, a reconstructed wetland to provide a natural habitat for native plants and wildlife.
74.3 Bloor Viaduct
75.4 Entrance to the Don Valley Brick Works Park.
Coleman, A.P. 1937.
Lake Iroquois in ODM Annual Report 45, part 7, p.5-6.
"The Iroquois beach has its most striking development at Hamilton, where it turns northeast. The western end of Lake Ontario has been cut off by a bar forming Hamilton bay. The ancient lake had a similar bar five miles to the west, cutting off a bay which may be named from the town on its shore, Dundas bay. The two bays are much alike in shape and area, but the floor of Dundas bay of Lake Iroquois is now mainly dry land, while the bar stands up as a very striking wall to the north of Hamilton. No finer example of a wave-built bar can be found than this great deposit of sand and gravel rising steep-walled more than a hundred feet above the level of the water. It crosses the valley as a causeway two miles long, giving an impressive entrance for the highway and railway into the city.
Originally the bar rose 116 feet above the present lake, or 302 feet above the sea, but it has recently been cut down a few feet in improving the Hamilton-Toronto highway [QEW]. Its width is less than a quarter of a mile at the base. Its lower part, when first studied by the present writer, consisted of well-stratified sand up to 57 feet, and its upper and steeper part was composed of fine and coarse gravel, often cross-bedded and usually cemented to a fairly resistant conglomerate."
p. 9 "The [Iroquois] shore follows closely the contour of 375 feet at first but gradually rises toward the northeast and approaches the 400-foot contour near Clarkson, where it turns northward toward a sharp bend of the Credit River. The river here has cut its way down 25 feet into grey shale, which has a few feet of boulder clay over it. To the west of the bend, near the Erindale school-house, a bar is seen between 325 and 350 feet. The southern end of it along the river has been cemented to a conglomerate, as may be seen from the Dundas highway. On the southeast side of the river bend another bar runs for a mile north and south and rises to the 400-foot contour. The first-mentioned bar must have been made in a bay of Lake Iroquois at a low-water stage before the later bar, which cut it off from the main lake, was begun."