This earthcache is located along Highbury Rd south of Highway 401, at one of the City of London Bulk Water dispensing stations. This location is accessible to the public and includes a parking lot and trails that go around the property. There are a couple of other caches on the trails to check out after visiting the earthcache.
Geology
Tyndall Stone, also called “Tapestry stone” is a distinctive mottled stone used in the construction or facing of many major buildings in Canada. The Houses of Parliament in Ottawa, the Legislative Buildings in Winnipeg (Manitoba), Regina (Saskatchewan) and the Empress Hotel in Victoria BC are prime examples. The material when fresh is a light grey with darker grey to brown mottles and it weathers over time to a pleasant creamy yellow or gold colour with rust coloured mottles. Fossils are always present in Tyndall Stone.
Tyndall Stone is quarried from Garson, Manitoba, which is located 37 km northeast of Winnipeg. The Garson deposit was opened in 1895, although the first record of construction with Tyndall Stone extends even further back to 1832, when it was used to build the fort warehouse and walls of Lower Fort Garry in Manitoba. Tyndall Stone acquired its name from Tyndall, the closest railway point to Garson.
During the late Ordovician Period, approximately 450 million years ago, southern Manitoba was a warm, shallow, inland sea just south of the equator. Many different types of animals lived in this ocean including corals, sponges, molluscs and algae. Other animals such as trilobites, and stromatoporoids are now extinct. These creatures lived on or above the soft muddy sea floor and when they died, their skeletal remains became part of the muddy layers. Other animals burrowed in the mud of the sea floor for food or protection and it is their preserved burrows that make up the beautiful mottling which gives Tyndall Stone its unique appearance.
A variety of fossil types can be found in Tyndall Stone. This earthcache will identify some of the types.
Trace Fossils: This is the name of the mottles which give the Tyndall Stone its distinctive appearance. The mottles are actually fossils. They are traces of burrows made in the original sediment by an unknown animal and the disturbed sediment within the burrows has been preferentially dolomitized at a later date making it darker and more resistant to weathering.
There is a noticeable colour difference between the mottle and the limestone surrounding it, as the mottles are mostly composed of finely crystalline dolomite (CaMg(CO3)2), and the surrounding rock is mostly limestone composed of calcite (CaC03). You should notice that the trace fossils or burrows are darker in colour than the surrounding rock, and on the outer exposed surface of the stones, these dolomite mottles are more resistant to erosion.
Tabulate and Rugose corals were ancient types not related to modern corals. They are now extinct.
Chain Coral (Catenipora) was a colonial tabulate coral. Individual corallites which form the colony grew as a vertical tube with elliptical cross-section and joined along the edges to give the appearance of a chain, hence the common name Chain Coral..
Horn Coral (Grewingkia) was a solitary rugose coral. Individuals were separate and grew in the shape of a slightly curved cone rather like a cow's horn, hence the common name Horn Coral. In cross-section the fossil shows a circular to elliptical shape with septa radiating from the centre. In vertical section it shows an elongated curved triangular shape with septa running along its length.
Receptaculitids were animals with a similar life style to modern sponges. They are now extinct. Fisherites was a large form which grew in the shape of a hollow irregular sphere, the walls of which were double and made up of small hexagonal plates and rods. In some sections the arrangement of the plates resembles a sunflower blossom hence the common, but erroneous name, Sunflower Coral.
Stromatoporoid - were colonial animals in which the very small individuals formed layers as the colony grew. They are now extinct.
Cephalopods/Nautiloid : These are relatives of today’s octopods, squids, and the “living fossil” nautilus. Like the existing nautilus they have a shell composed of a series of separate chambers. The shell may be curved (like the nautilus) or straight, but straight ones are much more commonly seen in Tyndall Stone.
Gastropods include your typical snails, as well as other forms such as slugs. Fossils of both tall spiral shells and more broadly rounded ones may be found in Tyndall Stone. Examples include the Hormotoma and Maclurites
Brachiopod are a group of lophotrochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs.
Saffordophyllum/Honeycomb coral was a colonial tabulate coral in which the vertical tubes of the corallites are polygonal in cross-section and joined on all sides to give the appearance of a honeycomb, hence the common name Honeycomb Coral.
To Log this Earthcache
Please send me your answers within 4 days of posting your found log. If there is more than one cacher in your party, include the names in your group. Only one person needs to send me the group answers. No spoiler photos, please. Found logs posted without proof you visited the site will be deleted.
There are a number of large fossils that can be found in this Tyndall Stone. You may want to start your search near the water fountains and expand out around the south and west side of the building. If you go around the corner of the building on the south side you will find some great examples of Stromatoporoidea.
Questions
- Look for and identify at least one fossil you find in the Tyndall stone wall. Tell me what type of fossil you found. Note: Your fossil can either be a trace fossil or body fossil from the examples given on the cache page.
- Take a photo of the fossil you find and estimate the length and width. Does the size of these fossils seem to be larger, or smaller than typical fossils found in Ontario limestone.
- Mandatory: Take a photo pointing to the Stromatoporoid shaped fossil that looks like some kind of strange white bird or what ever your imagination thinks it looks like. Post this photo along with your found log. See image on cache page showing the location of this fossil. It stands out! Note: Your face does not need to appear in the photo.
Resources
https://manitobamuseum.ca/main/the-fossils-surround-us/
https://tyndallstone.com/about-us/geographical-and-physical-findings
https://uwaterloo.ca/wat-on-earth/news/manitobas-tyndall-stone
