Like a Lost City
Just as a Victorian explorer, with pith helmet and machete, would suddenly come on an abandoned city deep in a Central American jungle, here, just off the beaten track, you suddenly emerge from a valley of scrub to be confronted by towering walls, like the defences of an ancient city.
This is the face of an abandoned limestone quarry, the largest of many in this area which, little over a hundred years ago, teemed with the activity of quarrying and processing limestone. Limestone was either quarried straight off the face of the wall or by excavation. One such shaft is visible in the picture.
The walls and buildings in this area are in an unstable condition. Do not attempt to climb or enter, and beware of the danger of falling rocks.
About 325 million years ago in the Carboniferous Period this area was a warm tropical sea south of the Equator. Apart from other sea life there were microscopic marine animals often with shelly, hard parts of calcium carbonate derived from the sea water. On death and by the gradual accumulation and compression over millions of years of these animals limestone was created.
This long quarry face shows a great number of bedding layers with each layer representing a change in the environment. The thicker layers imply a long period of quiet accumulation undisturbed by such events as storms or underwater earthquakes, while the thinner layers, some less than a centimetre thick, tell of short term events or “disturbances” like flooding on land and the increased flow of rivers into the sea. These flows from the land brought sand and mud. So here there are four main bedding planes, pure limestone, pure sandstone, pure mudstone and mixed layers where the limestone is mingle with sand and mud.
Many of our greatest building are of limestone but here the rock was too “contaminated” with sand or mud to provide the large solid blocks, colour consistency and resistance to erosion for such use. Much of the rock quarried here had to be discarded, but further along the wall you will come to a square kiln where the better limestone was converted into quick lime for the making mortar and whitewash and other uses. Unprocessed lime was also distributed over fields as a fertiliser where it reduced the acidity of the soils and improved crop yields.
To make quicklime the limestone was loaded onto grating in this kiln and heated from below. The resulting Quick Lime fell through the grating and was collected after cooling. The process was very energy intensive, about half a ton of coal was required to produce 1 ton of quick lime. The local abundant supply of coal here therefore made lime burning economically possible
Q1. The quarry face extends south-west about 400 m. What is the height of the quarry face at its highest point?
Q2. Explain the long mound opposite and extending the full length of the quarry face.
Q3. Please draw a field sketch of the quarry face at the highest point indicating possible examples of four bedding layers and their thickness of the following: mudstone, sandstone, limestone mixed with mudstone and sandstone, mixed mudstone and sandstone.
With your sketch please include title, direction faced, weather (this can affect rock colour appearance etc), scale (e.g. a coin/pen etc) and any 'wow' features that stand out etc)
Q4. Further along the path and across the tarmaced Colegate Road you will come on extensive quarry workings. Please examine the rockface at NT 3794 6174. Which of the following sedimentary features are visible here?
Coal seam
Cross bedded sandstone
Joints
Fossils
Purple or reddish mudstone
Please email me or send me your answers via the Message Centre, and a photo is always welcome. Your sketch needs to be photographed/ scanned and attached to your message.
This earthcache has been provided by the Lothian and Borders GeoConservation and in cooperation with the ranger service of Vogrie Country Park http://www.midlothian.gov.uk/info/200142/vogrie_country_park
For more information about the geology of this area why not go on these walk http://www.edinburghgeolsoc.org/downloads/GeologyWalk-VogrieCountryPark.pdf
http://www.edinburghgeolsoc.org/downloads/GeologyWalk-Crichton.pdf