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EarthCache

Rocks that Grew Earthcache

A cache by Hard Oiler
Hidden : 10/12/2004
In Ontario, Canada
Difficulty:
1.5 out of 5
Terrain:
1.5 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

This multi-virtual takes a short tour of a unique feature of the Lake Huron shoreline and explores the geological origins of the concretions that gave this place its name.


To take the tour, park close to N 43°12.741' W 82°01.355 and follow the path that leads below the point. Don't attempt to climb down from the top as you'll damage the bank. Follow the path and visit the following locations:

  1. N 43°12.729' W 82°01.380
  2. N 43°12.677' W 82°01.374
  3. N 43°12.674' W 82°01.369
  4. N 43°12.709' W 82°01.363


To log this cache as a find, visit each
waypoint and e-mail me the corresponding
picture letter. E.G. 1 = A, B, C or D; 2 = etc.
AND include in your email your estimate
of the diameter of the largest concretion
that you can find in the area

370 million years ago you would have been standing in a warm shallow sea, in a tropical climate, close to the equator. Layers of mud settling to the bottom of the sea, containing the remains of creatures and plants, eventually became the shale that you can see around you. The "Kettle" concretions (Latin - concrescere = grow together) were formed, while the layers of mud were still soft, by precipitation of calcite (calcium carbonate). As the crystals of calcite grew they pushed away the surrounding mud. Over time, the mud became buried and dried out and the concretions stopped growing. Here, at Kettle Point, erosion of the shale has exposed the concretions and you can see them as they appear from the shale as well as completely exposed on the shoreline and for some distance out on the shallow reef in what is now Lake Huron.

Such large spherical concretions are rare but similar, more recently formed ones, can be seen in New Zealand where they are called the Moeraki Boulders.

PICTURE A

Kettle concretions appear as the shale erodes. See how the shale folds around the concretion showing that it grew while the mud was soft. The dark colour is due to organic matter in the shale and is a source of the crude oil found locally.

PICTURE B

Some of the kettles grew as doubles or triples. This one looks like a hat and was formed when a new concretion grew on top of an earlier one. Note that the picture was taken in 2004 - note how time has changed it

PICTURE C

This kettle is split and shows the internal structure. Fibrous crystals of calcite radiate from the centre. The coloured rings of calcite result from growth under different conditions. Look for the rusty cracks on the surface. Iron sulphide (marcasite) was also precipitated and small (2=3 cm) marcasite concretions can also be found in the shale.

PICTURE D

The shale is jointed and split into large rectangular slabs. Note the finely laminated structure. Out in the lake, where the shale has completely eroded, the underlying limestone is similarly jointed and appears like giant paving stones



On a calm day a canoe or kayak is a great way to further explore the kettles in the shallows of the lake. You can park and launch from the beach at N 43°12.661' W 82°00.565'. You can also walk out into the lake but wear appropriate footwear as shale fragments can have sharp edges. See below for more pictures of kettles you can see out on the reef.


Multi-Concretion or sea monster?


This could be something from outer space!

Additional Hints (No hints available.)

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Inventory

There are no Trackables in this cache.

 

Find...

209 Logged Visits

Found it 204     Write note 4     Post Reviewer Note 1     

View Logbook | View the Image Gallery of 163 images

**Warning! Spoilers may be included in the descriptions or links.

Current Time:
Last Updated: on 10/15/2014 5:50:09 AM Pacific Daylight Time (12:50 PM GMT)
Rendered From:Unknown
Coordinates are in the WGS84 datum