James Bay, the place we call home, began as a deep oceanic lava plain formed during the Devonian period 370 million years before present (BP). Subsequent episodes of volcanism, erosion, sediment accumulation and crustal movement during the following 200 million years gave rise to the exotic terrane of Wrangellia that docked with North America 170 – 100 million years BP. The Pacific Rim and Crescent terranes followed, forming much of what is now southwestern Vancouver Island. Much more recently, at the peak of the Vashon stade of the Fraser glaciation 15,000 BP, James Bay was entombed by at least 1500 metres of ice; and a "mere" 1,000 years later, it was submerged by an advance of the sea: a marine transgression. After differential glacio-isostatic rebound and eustatic changes (changes in sea-level, not due to isostatic rebound, that occur worldwide), modern sea level was reached approximately 5,000 BP.

Surveying the shoreline just west of Finlayson Point, evidence of an ice-dominated environment evokes awe not only of the scale, but also of the endless variety of features. Referring to my well-worn and indispensable copy of The Geology of Southern Vancouver Island, by Yorath and Nasmith, I found numerous examples of metamorphic Wark gneiss bedrock exposures — a coarse-grained, banded rock resulting from high-grade metamorphism — that had been dramatically shaped into the asymmetrical roche moutonnée, a profusion of north-to-south-trending grooves and striations, and multiple crag-and-tail features that attest to the immense power of ice and entrained debris. Looking to the north, the sea cliffs in Beacon Hill Park along Dallas Road expose ice-contact gravels and Vashon till which accumulated adjacent to ice that had grounded in Juan de Fuca Strait about 12,000 BP.

My favourite feature is roche moutonnée, a reference to either the back end of a sheep or a barrister's wig. An example of stoss-and-lee terrain, it is rounded, smoothed, grooved, striated and polished by abrasion on the stoss, or upstream side, and steep, jagged and irregular on the opposing lee flank. According to Summerfield, increased ice thickness and higher pressures on the stoss (north exposure in this instance) side of obstacles decreases the melting point of ice (there is a decrease in the melting point of ice with increasing ice thickness of about 1°C per 1000 metres), creating a flux of basal meltwater which migrates to the zone of lower pressure on the lee side where it refreezes due to lower pressure, releasing latent heat of fusion. Depending upon the depth of joints in the bedrock, and facilitated by freeze-thaw cycles, blocks are mechanically pulled — or plucked — from the lowest to highest point in the rock floor when the basal ice freezes to them.

At the peak of the Fraser glaciation, which began 29,000 BP, the land was depressed by approximately 250 metres, and sea level was 100 - 150 metres lower than it is today. When the ice retreated about 14,000 BP, the ocean invaded all but the highest points of the Saanich Peninsula. This marine transgression completely covered James Bay, allowing for the formation of the Victoria Clay.

Glaciomarine Victoria Clay and Wark gneiss outcrops dominate the surficial geology of James Bay, while the Vashon till, which accumulated beneath the base of the ice sheet, overlies most of the bedrock. One can also find an isolated example of Holocene peat overlying Victoria clay on Niagara Street, between Rendall and Oswego. The clay, deposited at the close of the Fraser glaciation when the sea level was higher, is predominantly thick, soft, grey clay of more than 3 metres in depth. Of Jurassic age, the Wark gneiss outcrops have been potassium-argon dated from 131 - 182 million years of age. Comprised of massive and gneissic metadiorite—“meta” being the prefix used to denote metamorphism, while diorite is a coarse-grained plutonic igneous rock consisting of plagioclase and one or more of the ferromagnesian minerals—metagabbro and amphibolite, the Wark gneiss may have originally been composed of rocks of the Sicker Group and Karmutsen and Quatsino formations (Vancouver Group). James Bay Square and the Royal British Columbia Museum, for example, are constructed upon Wark gneiss, while most of the area bounded by Menzies, Belleville, Government and Dallas Road is underlain by Victoria clay.

For more information, please refer to these fine references:

Cannings, Sydney and Richard Cannings. Geology of British Columbia: A Journey Through Time. Vancouver: Greystone Books, 1999.
Fettes College. 2008. http://www.fettes.com/cairngorms [17 June 2008].
Ministry of Energy Mines and Petroleum Resouces. 2007. http://minfile.gov.bc.ca [14 June 2008].
Natural Resources Canada (NRC). Geoscape. 2008. http://www.geoscape.nrcan.gc.ca/victoria/index_e.php [20 June 2008].
Quaternary Geological Map of Greater Victoria. Map 2000-2. Victoria, BC: Ministry of Energy and Mines, 2000.
http://www.empr.gov.bc.ca/Mining/GeolSurv/Surficial/hazards/default.htm
Summerfield, Michael A. Global Geomorpholgy. New York: Longman Scientific & Technical, 1991.
Whittow, John. Dictionary of Physical Geography. London: Penguin Books, 1984.
Yorath, C.J. and H.W. Nasmith. The Geology of Southern Vancouver Island: A Field Guide. Victoria: Orca Book Publishers, 1995.

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