Drumbally Hill ASSI
| Site No | ASSI 328 |
|---|---|
| Area | 0.12 (ha) |
| Declared Date | 24/09/2010 |
| Confirmed Date | 19/04/2011 |
| County | Londonderry |
| Council(s) | Magherafelt District Council |
| Keywords | Geology |
Drumbally Hill is a special place because of its Earth Science interest. The area provides excellent access to an important exposure of limestone.
This exposure is what is left of a large quarry that once existed at the site. There are very few exposures of this rock left in the area. The limestone dates from the Carboniferous period of Earth history and is around 320 million years old.
Originally, the rock formed as a lime mud on the floor of a shallow, tropical sea. It was near a shoreline, however, that brought quartz sand grains and pebbles into the mud. Storms had the effect of removing some of the lighter mud particles, leaving a larger amount of sand grains than is usual for many limestones.
The exposure contains some fossil shell fish and crinoid fragments, also known as ‘sea-lilies’. These help to recreate the ancient environment and to place the rock in the right time period.
Limestones are usually quite pale in colour. At Drumbally Hill, however, many fresh rock surfaces show a red-brown colour. This shows the rock has been changed since it was deposited and it has likely been groundwater moving through once overlying rocks that caused this change in colour.
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