![]() View of the bluffs of drift near Port Stanley, Ontario. There were few areas where the proposed ice sheet could access the bedrock, to derive source materials for manufacturing the later drift, once the earliest drift layers were deposited. Since drift composition tends to resemble that of the local bedrock, the source cannot be some distant location. Access to source materials consisting of suitable rock types is required for the manufacture of the pebbles and boulders contained in coarse gravels in the glacial environment. But the materials that ice apparently over-rode were often unsuitable for producing these gravels. In many areas the ice must have over-rode silt, clay or sand, not dolomite or limestone bedrock. The bluffs at Port Stanley shown in the above photo illustrate this type of material. Boulders and pebbles of limestone and dolomite cannot be made from drift consisting of unconsolidated silt or clay. Access to suitable bedrock materials by the ice sheet would decline as more layers of drift were deposited. |
Relations of Drift formations in Southern OntarioRannoch Till (Huron Lobe) - silty clay, calcareous, overlies Tavistock Till.Stratford Till (Huron - Georgian Bay Lobe) - sandy silt, calcareous, overlies Tavistock Till and Mornington Till. Elma Till (Georgian Bay Lobe) - sandy silt and clayey silt, calcareous, overlies the Mornington Till. Mornington Till (Huron - Georgian Bay Lobe) - type section: Conestogo Dam. A brown or dark grey silty clay till, overlies Tavistock Till. Tavistock Till (Huron - Georgian Bay Lobe) - silty clay, coarse grained, coarsening towards Woodstock, calcareous, overlies Port Stanley Till, Stirton Till and Maryhill Till. Halton Till ((Erie - Ontario Lobe) - silt, overlies Wentworth Till. Wentworth Till (Erie Lobe) - overlies Port Stanley Till. Port Stanley Till (Erie Lobe) - clayey to silty clay, calcareous. It is thought to have been deposited over a period that spans all the above named tills. It occurs at the surface in the area of the Guelph drumlin field. Overlies Maryhill Till. Maryhill Till (Erie Lobe) - clay-rich, with sand and gravel. Type section, banks of the Grand River at Homer Watson Park. Overlies Catfish Creek Till. Stirton Till (Huron - Georgian Bay Lobe) - overlies Catfish Creek Till. Catfish Creek Till (Huron Lobe - southwest ice flow) - coarse grained, silty to sandy till, stony in some areas, compact, calcareous. Widespread in southwestern Ontario. Canning Till (Ontario or Erie Ice Lobe) - a reddish, fine textured till. The red color is attributed to its derivation from the Queenston Formation east of the Niagara Escarpment. |
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![]() Locations of Paleozoic bedrock formations below the drift in Southern Ontario. Map prepared using data from the Government of Ontario LIO site. |