Exposed units: Warren House Formation
The quarry lies on the northeast corner of Hangman’s Hill and 160m northwest of Dales Hall. About 12m of crag is exposed at present. Removal of the loose soil cover would easily expose more. The unit is a type of basalt called spilite (basalt that has been chemically altered by reacting with sea water) and is part of the Precambrian Warren House Formation. Rocks at the eastern end of the site preserve pillow lavas, further suggestive of the unit’s eruption under water. Sections through the pillows measure approximately 1m x 30cm, with a vertical long axis. During eruption, the long axis of pillow structures will be oriented in the direction that the lava was travelling and therefore will be lain down at an angle close to horizontal. Vertically oriented long axes in the current outcrop therefore indicate that that the Warren House Formation has been subsequently tilted away from horizontal. The top of the unit is present in the north side of the quarry, which comprises about 5cm of broken rock.
Platt, J.I., 1933, ‘The petrology of the Warren House series’, Geological Magazine, vol.70, pp. 423-429.
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