The resistant trachyte lava exposed at Skid Hill
A sketch map of the landforms of the Garleton Hills. Crag and tails (dashed lines) and major meltwater channels.
Lower Carboniferous trachyte lava flows at the top of the Garleton Hills Volcanic Formation forming the prominent scarp of Kae Heughs, Here, on the north face of the Garleton Hills, the lavas have been eroded to form a one-sided glacial drainage channel. The channel probably formed when meltwater was moved at high velocity through an ice tunnel. developed in dipping trachyte lavas. The dry gorge is cut along a fracture and into the underlying, softer basalts
A view towards the Hopetoun Monument from the east. Ice-moulding of the tough cores of the trachyte lavas, with streamlining towards the ENE. Several of these cores show a roche moutonnée form. Crag and tails are developed widely, including a particularly fine feature at Craigy Hill.
Significance: an ice-moulded ridge developed on Carboniferous lava flows of variable resistance
The Garleton Hills form a prominent ridge which provides extensive views over the lowlands of East Lothian. The hills are formed of layered volcanic rocks of variable resistance, elsewhere overlain and underlain by sandstones. The volcanic sequence has hard basalt overlying trachyte lavas.
Glacial erosion has exploited the differences in rock resistance. The trachyte lavas dip SSE and form ice-moulded cuestas or volcanic trap steps, with a steep scarp facing N and a short dip slope to the south. Ice and meltwater flow along the strike of the ridge has created furrows and meltwater channels. The low ground around Athelstaneford is a rock basin gouged partly from the softer basalts.