Prologue

Since 1998 Turnstone's office has been located in Campbellford, a town on the banks of the Trent river in eastern Northumberland county. This area of southern Ontario is dominated by rolling farmland and woodland, near the centre of a triangular region defined by Toronto, Ottawa and Kingston. Three distinct periods of geological time are beautifully displayed within the area. The Precambrian rocks of the Grenville province of the Canadian shield are exposed at intervals along Highway 7, within 20 km to the north of Campbellford. The immediate bedrock of the town is Ordovician limestones. A veneer of surficial deposits was brought, sculpted and left behind by glacier ice and associated drainage channels in the geologically recent past, in the Quaternary period. This economically-vital "skin" on the bedrock tops this grand layer-cake of history and provides many of the most accessible landscape features.

An illustrated summary of the natural history of the region is gradually evolving on this site. A township bird list of more than 100 species is now available, and serves as an index to selected local birds, beginning with an impressive, regular summer visitor, the osprey. Many of the more-common wild flowers, trees, and animals of the area can be found in a listing of the local flora and fauna.

To see an example of the fossils found in the limestones, click here. A compact bibliography of the geology and history of Campbellford and district is also available.

Introduction to Local Geology

1. The Grenville province of the Canadian shield represents the middle Proterozoic eon of Precambrian time, rocks formed relatively deep in the Earth's crust roughly 1200 million years ago. The Grenville forms the southeast marginal belt of the much larger Canadian Shield. It disappears from view in southwest Ontario, buried by a younger sedimentary platform to the south of a line that strikes west from the Kingston area past Tweed, Marmora, the northern Carden Plain and the north end of Lake Couchiching at Washago, into Georgian Bay north of Midland. However, it is part of a much larger geological province that is found from Scandinavia to South America, a large part of it forming the bedrock from Newfoundland through much of southern Quebec, southeast Ontario, and the Adirondack Mountains of upstate New York.

The ages of crystallization and recrystallization of these rocks can be estimated in a number of ways by the products of radioactive decay in suitable minerals. Thus the proportions of isotopes of lead in grains of the mineral zircon, formed in part by decay of isotopes of thorium and uranium, can yield precise estimates of the crystallization of magmas and episodes of heating and deformation in the crust. The shield rocks predominate north of Highway 7, which runs through or near such towns as Norwood, Havelock, Marmora and Madoc.

There are minor inliers of Grenville basement in northern Seymour township, within younger (Ordovician) cover rocks of the Gull River and overlying Bobcaygeon formations (see Section 2). Two such instances lie along the Crowe River drainage, just south of Crowe Bridge and around the bridge at Allan Mills (Carson, 1980). Bobcaygeon Formation rocks form the immediate bedrock from downtown Campbellford north to the confluence of the Trent and Crowe, while younger Verulam Formation limestones appear downstream, from Ferris park and Ranney Falls to the south. Thus the Precambrian rocks of the Canadian Shield appear at surface as close as 8.5 km N.N.E. of Bridge Street in Campbellford. They predominate north of a line through Tweed, Madoc, Deloro, Marmora and Round Lake, although small outliers of bedded limestone survive above the basement: a good example is found on a hill crest on the Havelock- Apsley road near Nephton.

The gabbro erratic on Grand Road

Many pebbles and larger blocks of Grenville rocks were carried down by the Laurentian ice sheets. A plaque was erected beside Grand Road in Campbellford, on 01 November 2002, celebrating a large and attractive example of erratic boulder in the IODE Parkette, composed of a striking rock type known as gabbro.

Geology and Minerals of the Grenville Province

The Grenville sector of the shield has a long and complex geological history. It contains a wide diversity of mineral deposits that were exploited, generally by small surface and shallow underground mines, in the 19th and early 20th centuries. Commodities include gold, lead, zinc, iron, molybdenum, uranium, and "industrial minerals" such as apatite (phosphate), feldspar, micas, graphite and wollastonite. Some operations continue to this day, across a wide region from Georgian Bay in the west to the Ottawa river in the east, and thence far to the east through southern Quebec to Labrador. Modern Ontario operations include mining and quarrying for talc, calcite, dolomite, building stones such as granite, and ornamental and semiprecious stones such as sodalite. Intermittent exploration continues to this day, for a range of targetted commodities such as base and precious metals and graphite.

This section will be expanded further as time allows!

Reference

2. The Ordovician limestones which lie unconformably upon the Grenville basement are often exposed in low, almost flat-lying outcrops along highways and river banks. Most bedrock outcrops in the region occur either along the unconformity between the Grenville basement and Paleozoic cover rocks, or along the major rivers such as the Trent (Carson, 1979). The Paleozoic strata are generally flat-lying, except where draped over irregularities in the Precambrian basement.

So-called "pop-up structures" are seen in three locations: northwest of Young's Point in the Gull River Formation, at King's Mill (Wellman) in the Bobcaygeon Formation, and near Woodview in the Gull River Formation. These are referred to as neotectonic features, meaning that they are of geologically recent (Quaternary) origin, presumed to reflect the relaxation and flexing of rock layers relieved, roughly 11,000 years ago, of the weight of the mighty Laurentian ice sheet.

The middle Ordovician is divided into five formations: the Basal Group is the shale, sandstone and arkose of the Shadow Lake Formation. The overlying Simcoe Group is divided into the Gull River Formation and Bobcaygeon Formation limestones, the Verulam Formation (limestone and shale) and the Lindsay Formation (limestone).

• The Gull River Formation is mainly lithographic limestone, often with stylolites and birdseye textures. Fossil cephalopods and stromatolites are common on bedding surfaces. Outcrops are abundant in Paleozoic outliers, and on the unconformity with the Grenville basement.
• The Bobcaygeon Formation is unevenly bedded and often flaggy. Fossils are common, especially brachiopods. Fist-sized nodules of black chert are abundant near the base.
• The Verulam Formation occurs as interbedded limestones and shales that form rubbly outcrops: fossils are abundant, including brachiopods, bryozoans, crinoids and rare trilobite fragments. The Verulam outcrops along the Trent and underlies the Rice Lake area without outcrop.
• The Lindsay Formation is generally pale to medium grey nodular crystalline limestone in shaly and rubbly outcrops: it is sparsely fossiliferous and rarely exposed (a small exposure occurs in the Ganaraska river in the town of Port Hope - it also occurs on the shore at Colborne and on the Presqu'ile peninsula).

This summary is derived from Carson (1979). The limestones have been explored in the past for lithographic stone, while modern quarrying extracts large tonnages for the chemical and metallurgical industries and for building and ornamental stones.

A casual reconnaissance of the limestones of the Gull River, Bobcaygeon and Verulam Formations of the Simcoe Group in the Campbellford area was initiated in 1998. Results to date suggest that brachiopods and bryozoans are the most widespread bioclasts, with lesser crinoid and rare trilobite fragments. Algal oncoliths are locally abundant. Accessory minerals include quartz and chalcedony, pyrite and goethite, and brown phosphatic collophane. Silica and pyrite are found in the lower formations, collophane in the younger Verulam Formation, and traces of iron oxyhydroxides are present throughout. In terms of a limited suite of field observations and reference samples, the micrite content (fine-grained facies of the limestone) falls from roughly 70 to 30 volume percent from Gull River to Verulam strata, and the bioclast proportion rises from 15 to 50 percent.

Suspension Bridge at Ranney Falls

The following illustrations of the local Verulam limestone depict a bluff of horizontal strata on the west bank of the gorge of the Trent river, near the south end of "Trent Island" and on the immediate south side of the outfall of the local hydroelectric power station. The bluff was selected as the site of the western end of what is now a fine pedestrian suspension bridge below Ranney Falls, linking Trent Island and Locks 11-12 of the Trent waterway with Ferris Provincial Park, on the east bank. The complex concrete-and-rebar foundations of the bridge were emplaced by the end of November 2002, and the span of the bridge was erected by contractors, including engineering specialists of the Canadian Armed Forces based at nearby Trenton, in the second half of the following year. The bridge was completed in the first half of December, 2003. Landscaping work at either end of the bridge preceded a well-attended official opening on 23 June 2004.

This addition to the local hiking trails will be significant, as the former railway grades are added to the nationwide system of the Trans-Canada Trail. The Trail and related links are now open eastwards from Campbellford to Stirling, Tweed and points east. Recent initiatives may soon open the westward section of the old rail line to Hastings: during November 2004 a local snowmobile club, the Percy Boom River Rats, was busy installing a bridge over a creek as part of a program of reconstruction along the line. A simple explanation of the bridge site follows, below the photographs.

The view on the left shows the top of the 12-metre-high bluff, looking north over Ranney Falls towards the town of Campbellford, represented by its water tower. Ferris park lies on the east bank (on the right in this image). At the centre is a small perched block of the limestone cap, ready to fall into the river below. This view is looking southeast from the site in the first photo, a few metres distant. The block is roughly 1 metre thick. On the right is a winter view of the gorge --- again with Laddie the dog for scale --- the area is an attractive outdoor destination year-round!

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Ranney Falls and the Trent River Gorge

This overlook provides a view of the Trent river at one of the more active sections of its course. The river's bed and sides, including the bluff on which you stand, are composed of horizontal layers of rock of middle Ordovician age. These beds are limestones with lesser layers of shale. The limestone contains fossils such as corals, bryozoans, crinoids and brachiopod shells. Known in southeast Ontario as the Verulam Formation, the limy sediments are believed to have been deposited in a warm, shallow sea roughky 460 million years ago.

The hilly terrain of Ferris Provincial Park, on the east bank of the river, was sculpted by the forces of the Laurentian ice sheet which retreated from this region some 12,000 years ago. The ice left its signature on the landscape, depositing silt, sand and boulders in the forms of whaleback hills (drumlins) and sinuous ridges (eskers).

Industrial Archaeology

Over here, within 10 metres of this spot, a careful hunt may reveal small pieces of bubbly slag and dense firebrick. One explanation is that these represent boilers associated with a tannery which operated on this bank, just upstream to the north.

The Suspension Bridge

The bridge was officially opened on 23 June 2004. The gentle arc of the metal walkway is some 93 metres (300 feet) long. At low water in the summer months, the centre of the walkway is at least 11 metres (36 feet) above the water level.

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The Limestones and their Fossils.

Three samples from the perched block, shown above, were taken for microscopic analysis. One of the samples from near the prow of the rubbly outcrop on the right is a brownish-grey bioclastic limestone with decreasing amounts of brachiopod, bryozoan and crinoid fossil trash. It represents a part of the Verulam Formation of the Simcoe Group, at the top of the middle Ordovician (Llandeilo age, circa 460 Ma). The rock contains decreasing proportions of sparry calcite, bioclasts, and fine carbonate (micrite), plus traces of detrital quartz and phosphate (collophane) replacing a small fraction of the shell material. A section through a bryozoan colony displays alternating structures, representing arrays of individual organisms in the colony, known as autopores (0.25-0.30 mm in diameter) and smaller mesopores (0.04-0.08 mm wide). The bryozoan is thought to be a species of the genus Prasopora. Brachiopods in the outcrop may include representatives of genera such as Strophomena and Rafinesquina.

Here is a photomicrograph of a colonial bryozoan in a sample of limestone from the bluff, showing the individual organisms that comprise the colony.

Sample 2359, bioclastic limestone. 40X magnification, long-axis field-of-view 2.8 mm, in plane-polarized transmitted light.

Reference

3. Quaternary Geology is a geological discipline which covers the past two million years of Earth history. Although this a short span in the development of our planet, roughly one twentieth of one percent of the estimated age of the Earth, the Quaternary is important to us in many ways. In higher latitudes, this period saw the waxing and waning of massive ice sheets which, at their full extent, stretched as much as halfway from the poles to the equator, and sculpted the landscape in many ways. The Quaternary incorporates both the past 10,000 years or so, the Holocene period, which includes all of recorded human history, and the much longer Pleistocene period which preceded it. Quaternary processes provide critical controls on water resources, and on the distribution of some of the "industrial minerals" necessary to modern civilization, such as sand and gravel deposits.

This section will be expanded shortly .

News Flashes / Archive of Local News

A bright meteor (commonly referred to as a fireball ) was spotted in the region by a few lucky people in the pre-dawn of 6th May 2001. Another example was seen over a wider area of eastern North America scarcely ten weeks later, in the early evening of 23 July, the so-called "Pennsylvania bolide" ).

Local Links

Here is a small selection of about 40 regional places, events and organizations. This is not meant as a travel guide, but simply offers a few clues to the commercial and recreational life and environment of the district. Many are within 20 km of Campbellford, and others are within longer day-trip range, such as Peterborough (roughly 50 km to the west), Bancroft (120 km to the north) or the Sharbot Lake area (150 km to the east).