Some important words to know:
Before I start with the earthcache, to keep it easy for every one, I have provided definitions of some words that some cachers may not know.
- Lineation - Lineations in structural geology (the study of the three-dimensional distribution of rock units) are linear structural features within rocks. There are several types of lineations, intersection lineations, crenulation lineations, mineral lineations and stretching lineations being the most common. Lineation field measurements are recorded as map lines. (More here: http://en.wikipedia.org/wiki/Lineation_(geology)).
- Faults - a fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement along the fractures as a result of earth movement. (More here: http://en.wikipedia.org/wiki/Fault_(geology)).
- Phosphate - Phosphate is an inorganic chemical, is a salt of phosphoric acid
- Bioturbation is the reworking of soils and sediments by animals or plants.
- Fossiliferous - Containing fossils.
- Karst topography - is a geological formation shaped by the dissolution of a layer or layers of soluble bedrock.
Hog's Back Falls:
From the posted coordinates, walk to bridge where it crosses the river. From here, look downriver. You can get a good view of the local geology. In the falls area are Middle Ordovician sedimentary rocks which have been faulted, gently folded, and tilted within small fault blocks as seen in the middle of the falls. Go to the observation area on the west side of the falls. From this point you can see an exposure of Rockcliff fm (Formation) sandstone. This is a fine to medium grained micaceous sandstone, and the grains are held in place by calcite. This sandstone contains more feldspar and lithic grains compared to the quartz-rich Nepean Fm. sandstone seen at http://coord.info/GC4QAH6. From here you can also see parting lineations.
Look east, across the river. You should be able to see beds of the Hog’s Back Fm. At the top of the cliff you can see overlying Pamelia Fm. (basal unit of the Ottawa Group). The Hog's Back Fm's bedding is thinner than the bedding for the Rockcliffe Fm., and is made up of argillaceous (clay-rich) dolostone, limestone and shale. The limestone beds display ripple cross-lamination and contain abundant fossils such as ostracods and bivalves and other skeletal fragments. The dolostone beds contain mud cracks and phosphate-rich burrows. Overtop of the Hog's Back Fm is the Pamelia Fm, at the top of the cliff section. It is made up of bioturbated and phosphatic sandstone, shale, and fossiliferous limestone beds. Exposures of the Pamelia Fm. further downriver, display abundant hemispherical stromatolites and, in some outcrops, good evidence of karst weathering.
An example of Karst weathering, (to the left).
There is a picture of a map below. Find the symbol of placed on the large island near the bridge. This symbol shows a strike; which is the intersection of inclined layers (e.g., bedding) with horizontal surfaces (here conveniently provided by the pools of water). The direction the rock is dipping is shown by a short tick on the side of the long strike line symbol. Examine the bedrock and make strike and dip symbols of your own.
The question you need to answer is this:
Draw your own strikes and dips. Like I said above, you should see a pattern emerge.
Tell me what pattern you see emerging. Send the answer to me by eMail, and DO NOT POST ANY HINTS OR SPOILERS ON THE CACHE PAGE PLEASE!
This information was compiled by Quentin Gall. 2010.