A Roadside Quarry
One day while driving along Mt Slide Road I noticed this abandoned roadside quarry. On investigation I decided that it would be a good spot for an Earth Cache that looked into Strike and Dip which are geological measures of the orientation or attitude of a geological feature.
Looking at the face of the quarry, it should be obvious that the rock is sedimentary and that in quarrying the rock, it has been split away along the natural layers or strata. We can make use of the exposed surface to measure the Strike and Dip of the sedimentary rock. To do this you will need some tools… if you are really into the geological sciences you may already have something like a Brunton compass or a Stratum compass but you don’t, an ordinary compass, a spirit level and protractor will be quite adequate… as will any one of a number Smartphone apps as I have used.
The Strike (angle) is the azimuth compass bearing of the Strike Line of the rock bed which is a line representing the intersection of the surface of the rock bed with the horizontal plane. To explain that in more practical terms, imagine (and please use your imagination, don’t go defacing the rock face) a horizontal line drawn on the exposed rock face… that is the Strike Line. The Strike is the compass bearing of that imaginary line measured in the horizontal plane (or azimuth). Note that the Strike is usually expressed as the lower of the two possible numbers i.e. 50o rather than 230o.
The Dip is the steepest angle of decent of a tilted bed or feature relative to the horizontal plane and is measured in degrees between 0o and 90o. When a sedimentary rock bed is laid down, the Dip would be 0o i.e. the rock bed is not tilted. Here in the quarry, the Dip is the angle of the exposed face to that imaginary horizontal plane.
To log this Earth Cache I would like you to answer the following questions. I suggest you use the west face of the quarry as it is reasonably easy to get to and that is where I made my measurements.
Questions:
- What do you measure the Strike of the rock face to be?
- What do you measure the Dip of the rock face to be?
- Given that sedimentary rocks are relatively soft and the distance that this quarry is from any significant township, what do you think the rock from this quarry was used for?
Please send your answers to me using the Message system or e-mail. You are welcome to log this cache after you have visited to keep your records in order but please don’t make me chase you for your answers. If I haven’t heard from you in a week (even a simple request for more time will do), your log may get deleted.
You are welcome to add photos to your log but please make sure that don’t give any of the answers away.