Healey Dell. Shales and thin sandstone concretions EarthCache
Healey Dell. Shales and thin sandstone concretions
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Healey Dell,is a local nature reserve that lies in a valley to the north of Rochdale. the River Spodden runs through the valley. It is a place of great flora and fauna, but also of geological interest.
Here at the side of the track is an easily accessible evidence of shales and thin sandstone flattened concretions.
As you look the rock, you can see layers of rock, some of it very thin and friable - the shale, with other thicker layers - the sandstone. You will also notice mishapen rocks of sandstone amongst the shale, these are what is known as concretion.
Concretions are found in a variety of rocks, but are particularly common in shales, siltstones, and sandstones. They often look like rocks that appear to not belong to the layers they are in. In the talk of the man on the streat - they look different. They appear in nodular patches, concentrated along bedding planes, protruding from weathered cliffsides. A concretion is a volume of sedimentary rock, where spaces between the sedimentary rocks are filled with 'cement'. They are often round or egg shaped, but can be irregular.
There have been theories about how they are formed, such is discussed by Hanson (1994) who explains that a study in 1957 suggest that concretions were formed after the time that the shale was being deposited, but before it was completely compacted.
These rocks were laid down in the far distant past, at a time known as the Lower Coal Measures of the Carboniferous era, when this area was a vast delta, with rivers laying down sand, rock and clay in layers known as sediment.
Shale is really ancient dried mud, which has been hardened by pressure, and acqures a thin layer appearance. Its dark colour is due to the amount of decayed vegetation in it.
References
Hanson, M (1994).Ohio Shale Concretions. Ohio Department of Natural Resources. Division of Geological Survey.
Bolton (1890). The Geology of Rossendale.
To log this earthcache , please contact Hillgorilla, with the answers to the following questions:
(1) What does the shale feel like?
(2) What do the concretions feel like ( please just touch, there is no need to remove any).
(3) What colour is the shale and the concretions.
(4) As an option, please take a photogrpah of -
(i) Yourself or GPS at the site
(ii) Concretions.
(iii) Shale.
Additional Hints
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