The rocks along the Manigotagan River are millions of years old and are part of the massive rock craton that forms the core of the North American continent, the Canadian Shield. The landscape is rolling and characterized by rock outcrops that were rounded during the last ice age. The break-down of the ancient rocks create the soils that support the plants of the beautiful boreal forest.
The rocks that you will see while paddling along the Manigotagan are igneous, volcanic or metamorphic in origin. Check out the "Geology - Rock Types" layer on the interactive map to see where to generally find different rock types (you may find that small areas differ from the map due to "map generalization" - Granite gates is such an example). Check out the "Geology - Origin" layer on the interactive map to see where to find igneous rocks of different ages. The following table and descriptions will help you understand what these layers show.
Table 1: Common rock types in the Manigotagan area and their origin.
| Rock Type | Origin |
| Granite | Igneous/Plutonic |
| Gabbro | Igneous/Plutonic |
| Tonalite | Igneous/Plutonic |
| Basalt | Pyroclastic Volcanic |
| Andesite | Pyroclastic Volcanic |
| Gneiss | Metamorphic |
| Migmatites | Metamorphic |
| Greywacke | Metamorphic |
| Metavolcanic | Metamorphic |
| Metasedimentary | Metamorphic |
Igneous/Plutonic Rocks
Igneous rocks are formed from molten magma. The word, igneous means "fire". They are also called plutonic rocks. All igneous rock starts deep in the earth as hot, molten magma. If the magma cools and hardens inside the earth it forms intrusive igneous rock. These rocks cool slowly and have large mineral crystals (you can see them with your eyes). The pink granite, the gabbro and tonalite are examples of plutonic rocks.
If you look carefully you will see that these rocks have many different colors in them - even the pink granite. The color reflects the different minerals that make up the rocks. Different combinations of minerals make different types of rocks (granite, granodiorite, syenite, etc.).
Pyroclastic Volcanic Rocks
Basalt and andesite are pyroclastic volcanic rocks. This means that they originated from lava (magma that has come to the earth's surface) and cooled much faster than the igneous rocks, which cooled at greater depths. The fast cooling process prevented the minerals from forming larger crystals (those that can be distinguished with the bare eye) and these rocks appear to be more homogenic in colour.Metamorphic Rocks
Metamorphosis is a geological process during which rocks undergo dramatic changes due to high pressures and/or temperatures. The resulting rocks may have a very characteristic "layered" or "folded" look (as shown on left). Gneiss, migmatites, greywacke metavolcanic and metasedimentary are metamorphic designations. Gneiss, Migmatite are names of metamorphic rocks and Greywacke, Metavolcanic and Metasedimentary are more of a metamorphic description.
This region of Manitoba is also noted for having a "Greenstone" belt. The greenstones are typically dark in color and the belt contains ore deposits of gold. Through contact metamorphism (local melting of the rocks through heat and pressure) of the local greenstones the gold ore have become concentrated enough to mine. In fact, there was an Eastern Manitoba Goldrush in the early part of the 20th century (See section on Mining). When you see rocks that are black or dark green on the side of the river, they probably belong to the greenstone belt. Keep your eyes open for shiny minerals. However, if you find minerals that are golden in colour and shiny, they may not be gold but pyrite. Pyrite is also known as "fool's gold", because it fools people: it very much looks like gold, but does not have its other qualities and is not as valuable.
With thanks to Kim Monson, The
University of Winnipeg, Geography Department. January 2007.
