2.3 Glacial History

The glacial history of south east Scotland has been the subject of significant interest from geologists and palaeoenvironmental specialists. This interest has, however, been unevenly distributed both spatially and temporally. The glacial advances and the wasting patterns of the Lower Tweed Valley and the Firth of Forth have figured prominently because of the salience of some glacially distinctive landforms (Burke 1969; Everest et al 2005; Kirby 1968; Sissons et al 1966; Staines 2009). Both regions have also been important in the study of the dynamics of the British ice-sheets (Boulton et al 2002; Clark et al 2004; Clark et al 2012; Hughes et al 2010; Hughes et al 2014; Jones and Keen 1993).

Conversely, the glaciation and melting of the ice-sheets between these landscapes has elicited little attention and have all too often been consigned to the descriptive memoirs accompanying the geological maps produced by the British Geological Survey, or have been the topics of doctoral theses (eg Alexander 1985; McAdam and Tulloch 1985). The exceptions to the latter are largely older studies (Kirby 1968; Young 1966), but the research on the chemical attributes of the soils to investigate glacial ice-sheet movement represents a new direction of inquiry (Stone and McMillan 2013).

Some excellent research has been undertaken on landforms at the boundaries of the SESARF region, such as the Southern Uplands and the Cheviot Hills, and in the upper reaches of the Forth Valley. In the Southern Uplands, the glaciation and subsequent deglaciation process has been studied across a wide region that includes not only Dumfriesshire and Lanarkshire, but also the Lake District of England (Finlayson et al 2010; McLellan 1969; Pearce at al 2014; Sissons 1969). The Cheviot Hills do not encompass such a broad area as the Southern Uplands, but their study has possibly been far more intensive and diverse because of the existence of an independent ice-sheet here. Its growth, dynamics, and ultimate wastage have intrigued geologists for decades, and there is thus a correspondingly large corpus of research concerned with this landscape (eg Mitchell 2008). Understanding the glacial ice-sheet dynamics of the Forth also renders it necessary to look beyond the spatial orbit of the south east of Scotland and into West Lothian, Stirlingshire, and Fife (Cullingford and Smith 1966; McCabe et al 2007; Sissons and Rhind 1970).

Photograph looking up at the cheviot burn. The ground is hilly and marbled with snow.
The Cheviot Burn, Morebattle © Walter Baxter (CC BY-SA 2.0)

Ice-sheets advanced into the Scottish Borders from two directions. A glacier with origins in the uplands around Cairnsmore of Carsphairn flowed eastward and north-eastward around Broad Law towards The Merse (Berwickshire) and Firth of Forth, respectively (Greig 1971, 97). The second glacier originated near Loch Lomond and flowed into the Firth of Forth, turning southward to follow the North Sea coast. It was the former ice stream, however, that wrought the glacial features near St Boswells and whose wastage resulted in the deposition of copious quantities of sand and gravel throughout the landscape. This stream moved quite fast – this is evidenced especially well by the elongated drumlins that are found along the course of the River Tweed between Kelso and Berwick-upon-Tweed, which formed at the margins of a fast-moving current of glacial ice (Everest et al 2005, 166–9).

Drone photograph of snow-dusted mountains
Cairnsmore of Carsphairn with Beninner in the foreground, looking NW © HES

Many of the superficial deposits have their origins in the advance or wastage of the ice-sheets. It seems that this part of Scotland experienced glaciation sometime around 26,000 BP, but it should be recalled that there might have been significant regional differences in ice-sheet extent for studies in Buchan interstadial deposits dating to between 26,000–22,000 BP (Jones and Keen 1993, 171). Better dating of the glacial advance into the Scottish Borders is therefore necessary. A similarly problematic matter is the dating of the glacial ice-sheet wastage in the region. Most of the statements pertaining to this are based on research undertaken elsewhere in Scotland, rather than in the SESARF region itself, so their accuracy is difficult to assess.

In recent syntheses Ballantyne and Small (2018) and Ballantyne (2018) highlight that deglaciation was a diachronous process across Scotland, occurring between 21,000 and 14,000 BP. Whilst most of Scotland was likely still glaciated around 17,000 BP, parts of the eastern seaboard may already have been ice-free, with the southern lowlands ice-free around 16,000 BP. However, some perplexing early dates for deglaciation have been acquired for sites in Strathmore; these affix the deglaciation process to c. 22,000 BP (McCabe et al 2007, 315). This date agrees with those for the interstadial deposits identified in Buchan and a series of dates from the Irish Sea littoral, but disagrees fundamentally with evidence derived elsewhere in the British Isles (Clark et al 2012, 133–7).