The glacial stratigraphy of the Midlothian basin after Kirby (1968)
Poorly-exposed inter-bedded till, sand and gravel along the Keith Water.
On the main tools for reconstructing the glacial history of an area is to examine the local stratigraphic record. Tills are firm indicators of the former presence of glacier ice and the their fabrics and erratic content provide information about the direction of former ice movement. Where tills are interbedded with other sediments, such as meltwater or periglacial deposits then a sequence of events can be built up.
The glacial history of Edinburgh, Midlothian and East Lothian received detailed attention from the pioneers of glacial geology seeking to understand the pattern of flow and behaviour of former glaciers. By 1840 the main indicators of flow of the last ice sheet had been identified and mapped. Thereafter interest waned until the 1960s when Roger Kirby began to look at the sequence of glaciation in Midlothian. Kirby (1968; 1969) identified a tripartite glacial sequence in Midlothian:
Till C rests on bedrock. It contains erratic stones carried from the west and shows till fabrics which are also consistent with ice flow eastwards parallel with the Firth of Forth. It is locally overlain by bedded sand.
Till B contains many stones of greywacke from the Southern Uplands. Till fabrics indicate deposition by ice moving SW-NE or S-N towards the Firth of Forth. Till B is also overlain by bedded sand, with ice wedge casts on its upper surface, indicating the former presence of permafrost.
Till A is confined to the area around Roslin. Fabric measurements indicate that it was deposited by ice moving N-S or S-N. The Roslin Till may relate to a late lobe of ice from the Firth of Forth that pushed into the low ground beside the Pentland Hills and ponded meltwater ahead of it.
The terrain of the Midlothian Basin and the corrugated slopes of the Lammermuir Hills are suited to the trapping of glacial sediment. Glaciers advancing from or retreating towards the Forth would have poured meltwater into any ice-free areas inland. The higher ground of East Lothian thus has the potential to retain complex sequences of glacial and fluvioglacial deposits. It may be that this complexity has yet to be recognised due to a combination of limited recent work, poor exposure and and absence of dating control.
East Lothian links
Glacial stratigraphy in other parts of Scotland