Signs of the Past EarthCache
Hidden : 6/1/2014
Difficulty:
1.5 out of 5
Terrain:
1 out of 5

Size: Size: other (other)

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Geocache Description:

Many people walk past these buildings every day, but not many stop to look at what they're made of. Have you?

Limestone is commonly used as building stone in North America, but Tyndall Limestone is unique. The colour, beauty, strength and durability of Tyndall Limestone has allowed for it to be used in a variety of ways and architectural styles. Tyndall Limestone is used extensively as an ornamental building stone across Canada. Tyndall Limestone is building stone from the Selkirk Member of the (Ordivician) Red River Formation. The best exposures of the Tyndall Limestone are found in the Garson-Tyndall area, approximately 30 km northeast of Winnipeg, Manitoba. The small village of Garson, Manitoba bills itself as The Limestone Capital of North America. The name of the stone comes from Tyndall, the closest railway point to the quarries; the railway station was itself named after the noted British physicist Professor John Tyndall.
Tyndall Limestone is a fine grained light coloured, fossil-bearing limestone with comparatively darker brown coloured fine to medium grained medium tubular-shaped branching network of dolomitic limestone, which give the rock a mottled appearance.

Two major types of fossils occur in Tyndall Stone. The first are body fossils (shells, etc.) and the second are trace fossils that occur as a pervasive network of burrows.

Body Fossils Body fossils are the hard, shelly remains of organisms preserved within a rock. The following is a non-inclusive list of the most abundant fossils you may find:
Cephalopods - are like modern squids or nautili. Cephalopods with straight shells are called Orthocone, whereas those with a curved shell are known as Winnipegoceras.
Gastropods - are more commonly known as snails and slugs. On a cut surface, the fossil may have a coiled appearance.
Chain Coral - are colonial coral that have an irregular grid pattern that sometimes resembles a distorted chain-link fence.
Horn Coral - is a solitary coral. In the rock the fossil has a pattern of line radiating out to an oval or a horn-like pattern.
Sunflower Coral - are the largest and most enigmatic of the Tyndall fossils. These aren't actually corals, but calcareous algae. The fossil occurs as a circular colony, characterized by a uniform grid pattern and a distinguishable deep hollow in the centre.
Brachiopods and trilobites - may also be present but are more difficult to identify.

When examining the rock for fossils, keep in mind that the shape of the fossil displayed may vary considerably depending of the random cross-section on the exposed surface of the building stone.

Trace Fossils The shell-type fossils are intriguing, but it is the trace fossils that make this limestone an attractive building stone. Unlike body fossils, trace fossils are fossilized tracks, trails, or burrows left during the day-to-day life activities of an organism. The trace fossils are evident as a mottled texture. This image is a schematic block diagram of what the network of burrows might look like in three dimensions.


The difference in colour between the burrows and the rock outside of the burrows is due to differences in the grain size and chemistry. As the burrows were created, it's assumed the animals lined their burrows with slime to add strength, much like today's modern earthworms. Additionally, the dirt left behind in their burrows was loosened and replaced compared to the mud around the tunnels.

In order to log this cache, you must email me with:
- Your estimate the average thickness of the burrows;
- The type and size of the largest body fossil you find, as well as it's GPSr coordinates as given by your device;
- Walking the length of the building, what is the most common fossil you find (other than the tunnels)?
- OPTIONAL - Take a picture of at least one uncommon body fossils with your GPS for scale and identify it, posting both in your log..

As an added bonus, there are other buildings in downtown Lethbridge which also have the same stone. Feel free to look as you geocache the area!

Logs without an accompanying email will be deleted.

Congratulations to Joci for the First To Find!

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