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Geology at the Howe (Walk 8)

The rocks are classified according to the minerals they contain. Basalts and andesites are richly charged with iron oxides such as haematite, and are seen in the characteristic dark-red screes and outcrops found beside the lower part of Flotterstone Glen road (Walk 24). Rhyolytes and trachytes tend to be pink or pale orange in colour. Rhyolyte can be seen on the summit of Caerketton Hill (Walk 1) and trachytes are best seen on Torduff Hill (Walk 4). Tuffs, pale in colour and often containing distinct fragments of other rocks, can be found on the summit of Carnethy Hill (Walk 21).

The rocks of the Upper Old Red Sandstone age are found around West and East Cairn Hills (Walks 11 and 15). Earth movements during the Lower Carboniferous period created the Pentland Fault (the A702 follows the line of the fault), which separates the Pentlands from the Midlothian coalfield.

Mendick Hill from the Roman road (Walk 13)

The rounded profiles of the hills, the deposits of boulder clay and striated (scratched) rock surfaces, are evidence that an ice sheet scoured the Pentlands. In the last two million years, warmer spells between ice ages caused the ice to melt, and vast quantities of meltwater cut out channels to lower ground. Green Cleuch (Walk 9) and the area to the west of Carlops (Walk 16) are excellent examples of these meltwater channels.