Presqu'ile tombolo

Presqu'ile is a tombolo on the north shore of Lake Ontario in Northumberland County.[1] When proglacial Lake Iroquois drained, leaving the lower Lake Ontario five limestone islands, the largest of which was Presqu'ile Island reduced the speed of currents carrying sand and silt, causing the dynamic sand spit to grow. The spit eventually engulfed Presqu'ile Island, and two small islands. Gull and High Bluff islands remain unattached,

The Tombolo and the two remaining islands form Presqu'ile Provincial Park, and provide a temporary sanctuary for migrating birds.[2]

References

"Geology and Formation of Presqu'ile". Friends of Presqu'ile Park. Archived from the original on 2019-05-06. Retrieved 2019-05-06. In the last few thousand years Lake Iroquois drained somewhat to form our present-day Lake Ontario. As it did so, five islands appeared off-shore of the mainland. These islands are comprised of limestone, part of that package of rocks formed so long ago in the Ordovician. This limestone has now been designated as part of the Lindsay Formation and is described as thin, crystalline to nodular limestone with very thin shaley seams (Peterson, 1969). This means that the rocks break up quite easily and form the low rubble cliffs found today on the south shore of Presqu'ile. This also means that the rock is not very suitable for building stone as demonstrated by the fate of the Presqu'ile Lighthouse (see the History section here). This rock is full of fossils, primarily crinoids, brachiopods, trilobites, and cephalopods, in decreasing order of abundance. Most of these fossils are fragments of the animals' shells, as they probably tumbled down a slope on the sea bed before coming to their final resting place to begin the process of fossilization.
"Presqu'ile Provincial Park". Geographical Names Data Base. Natural Resources Canada. Retrieved 2013-05-12.

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[friendsofpresquileGeology-1] "Geology and Formation of Presqu'ile". Friends of Presqu'ile Park. Archived from the original on 2019-05-06. Retrieved 2019-05-06. In the last few thousand years Lake Iroquois drained somewhat to form our present-day Lake Ontario. As it did so, five islands appeared off-shore of the mainland. These islands are comprised of limestone, part of that package of rocks formed so long ago in the Ordovician. This limestone has now been designated as part of the Lindsay Formation and is described as thin, crystalline to nodular limestone with very thin shaley seams (Peterson, 1969). This means that the rocks break up quite easily and form the low rubble cliffs found today on the south shore of Presqu'ile. This also means that the rock is not very suitable for building stone as demonstrated by the fate of the Presqu'ile Lighthouse (see the History section here). This rock is full of fossils, primarily crinoids, brachiopods, trilobites, and cephalopods, in decreasing order of abundance. Most of these fossils are fragments of the animals' shells, as they probably tumbled down a slope on the sea bed before coming to their final resting place to begin the process of fossilization.

[CGNDB-2] "Presqu'ile Provincial Park". Geographical Names Data Base. Natural Resources Canada. Retrieved 2013-05-12.