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Soft Rock and Hard Rock

Geologists in the 19th century did not dig deep into the ground to try to find oil or minerals. Travelling long distances through Canadian wilderness, they made most of their observations by studying the rocks and fossils they found at the surface.

Sketch from a William Logan notebook of various rock layers

Sketch of rock strata from William Logan's notebook

How does a geologist figure out what bedrock lies underneath the soil, especially when the ground is covered with plants? Sometimes a geologist is lucky and can observe the geological structure directly. In the Rocky Mountains geologists can do that. Most often, however, they can only see outcrops (exposed rock) of the rocks that lie below the surface. This is what the "Rock Stars" found when they were exploring the southern parts of eastern Canada.

Photograph of a crinoid fossil (animal related to the starfish)

A rare crinoid fossil
(animal related to the starfish)

Geologists have to use all the clues they can find. Younger layers of sedimentary rocks are usually found on top of older layers. This is true except in a few tricky cases where the earth's forces have turned things upside down over millions of years. Usually though, rocks are found in layers that can be traced from one area to another. You might find a certain rock in two different places and know that they are connected as one rock formation. Rocks sometimes contain fossils. If you find the same fossils in two different places, then you have found rocks of the same age.

Photograph of carboniferous rocks and fossil trees in Nova Scotia, 1879

Carboniferous rocks and fossil trees from Joggins, Nova Scotia, 1879

William Logan and his crew were looking for coal. Coal is found in sedimentary rocks, which exist in southern Ontario and Quebec. No wonder the Geological Survey of Canada was hoping for rich coal deposits there. Logan was able to prove very quickly that there was no coal because all the rocks in that area were too old and lay well below the coal-bearing carboniferous formations. Knowing this saved lots of time and money in useless digging.

Harder to figure out were the metamorphic and igneous rocks that make up the Canadian Shield. These rocks do not contain oil or coal, but do often contain lots of minerals and metal ores. Logan and his assistants took a look at these rocks, but they were not studied closely until the late 1800s and early 1900s.

Digging Deeper

Three Rock Groups

The Earth's crust contains elements (oxygen, iron, calcium, silicon, etc.) These elements combine in different ways to make minerals. Rocks are made of minerals.

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Digging Deeper

Making Your Bed Rocks!

Diagram of bedExplore this Topic

In His Own Words

"I do not describe fossils, but use them. They are geological friends who direct me in the way to what is valuable. If you wish information from a friend, � you merely recognize his face, remember his name, and interrogate him to the necessary end. So it is with fossils."

(William Logan, testimony before Select Committee of the Legislature, 1854)

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Geological time chart

Geological time chartExplore this Topic