This platform is for the temporary display of other rocks that have been collected close to home or at distant locations.

The story of the first guest rock is about one of the oldest and longest known ice ages on Earth.  The tale of the second is about colliding continents and rocks formed deep in the roots of towering mountains.

Gowganda Conglomerate

Sample courtesy of Dr. Allan Donaldson.

Gowganda Conglomerate Web Page Photo 2

Photo courtesy Metcalfe Geoheritge Park Committee.

Gowganda conglomerate is composed of rounded cobbles and pebbles of pink granite and other rocks in a fine-grained grey mud.  This sample is from the Elliot Lake area of Ontario.  It’s of middle Precambrian age, about 2.3 billion years old.

The Gowganda Formation of northern Ontario, discovered in 1905, was originally a poorly sorted sediment that was deposited (i) under an ice sheet, and (ii) when glaciers flowed down to a cold sea and dumped debris downslope on the ocean floor.  This took place about 2.3 billion years ago during the Huronian ice age, one of the most severe and longest ice ages in geological history.  Paleomagnetic evidence indicates that the Huronian glaciation occurred at tropical latitudes.  This discovery led to the Snowball Earth hypothesis that our planet’s surface was nearly or entirely frozen.

The glacial till and seafloor sediments were later buried, compacted under pressure, and gradually became solid rock.  This short video about the Gowganda Formation is from the American Museum of Natural History.

Mica Schist

Sample courtesy of David Garcia, Michel Gauthier, and Rick Scholes.


Photo courtesy Metcalfe Geoheritge Park Committee.

Mica schist from the Grenville Province of the Canadian Shield in Lanark County.

Schist (pronounced shist) is a medium-grade metamorphic rock with platy and elongated minerals, such as micas and talc.  Mica schists are rich in mica minerals, such as biotite (black) and muscovite (silvery in this sample).  The individual mineral grains are scale-like flakes which reflect light, giving the rock a shiny appearance.  The word schist is derived from the Greek word meaning “to split”.  This refers to how easy schists can be split along the plane in which the platy minerals lie.

Mica Schist Web Page Photo 4

Photo courtesy Metcalfe Geoheritge Park Committee.

Look closely to see the tiny flakes of mica which reflect light and give the display rock its shiny appearance.

Most schists are created from sedimentary shales that have been metamorphosed by heat and pressure.  Some schists are derived from fine-grained igneous rocks, such as basalts and tuffs.

About a billion years ago, during the Precambrian Super Eon, continental collisions pushed igneous and sedimentary rocks up and over the eastern continental edge.  Layers of rock were folded, invaded by magma, and pushed skywards to form the Grenville Mountains.  A modern example is the Himalaya Mountains formed by India colliding with Asia.

Deep in the mountain roots, at depths of 20 km or more, metamorphic rocks were created under high temperature and pressure.  Limestone was changed to marble.  Mica schist was formed from shale.  These and other Canadian Shield rocks are now exposed at the surface in Lanark County west of Almonte.

Guest Rocks Glossary
  • conglomerate    a sedimentary rock consisting of rounded fragments of pre-existing rock within a finer-grained sedimentary matrix
  • igneous rock    formed from the solidification of magma
  • mica    a group of silicate minerals that form in flexible sheets and flakes, such as biotite, muscovite, phlogopite
  • Precambrian Super Eon    the earliest of the geological ages, from the formation of the Earth about 4.6 billion years ago to the beginning of the Cambrian Period, about 540 million years ago
  • shale    a fine-grained sedimentary rock formed from mud
  • sedimentary rock    formed by (i) cementation of sediment, such as sand or mud, (ii) precipitation from water, such as salt, (iii) consolidation of plant material, such as coal
  • till    an unsorted glacial sediment

Helping Hands

Gowganda Conglomerate Web Page Photo 1

Photo courtesy Metcalfe Geoheritge Park Committee.

The transportation and placement of our guest rocks has been a team effort.  Calvin Murphy, Mississippi Mills Recreation Coordinator, was on hand when the display pads were ready.

Mica Schist Web Page Photo 2

Photo courtesy Metcalfe Geoheritge Park Committee.

Although the mica schist was a relatively thin sample, the large rock required many hands to load.

Mica Schist Web Page Photo 1

Photo by Rick Scholes.

A team of local volunteers assembled at a roadside outcrop to collect the mica schist.  Left-to-right:  Rick Scholes, Michel Gauthier, Neil Carleton, David Garcia.

Guest Rock Nomination

Please get in touch if you have a large rock of interest for temporary display.

Metcalfe Geoheritage Park, P.O. Box 400, Almonte, Ontario, K0A 1A0


To access the web pages of other display rocks, you can also use the drop down menu on the website’s navigation bar.

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