Callander & Keltie Water: A landscape of ancient rivers and glaciers

Follow the Callander Geodiversity Trail and learn about ancient river floods and evidence of former glaciers, and enjoy picturesque waterfalls

Bracklinn Falls Circuit and footbridge. Almost vertical strata cut perpendicularly across by the powerful Keltie Water. Image: Mike Browne.

Callander, gateway to The Loch Lomond and Trossachs National Park, is located a little over 2 kilometres south-east of the Highland Boundary Fault that crosses Scotland from the south-west (Arran) to the north-east (Stonehaven). To the north of the Fault are cooked, stewed and heavily deformed metamorphosed sandstones and mudstones (schist and slate). These rocks were laid down as sediments in the southern hemisphere’s Iapetus Ocean, which existed more than 480 million years ago. Evidence for this can be seen in the fossilized marine shells found in the limestone above Callander at Leny Quarry. Major Earth movements completely closed the ocean and gave rise to ancient ‘Grampian Highlands’, which were largely eroded away by 420 million years ago.

On the south side of the Fault, you can follow the leafleted Geodiversity Trail and see the thousands of metres of sedimentary and volcanic rocks that were deposited in the area from about 415 to 400 million years ago. At that time, Callander was about 30o south of the Equator. Sediments were deposited mainly in a semi-arid (sometimes desert) environment. Rivers carried enormous volumes of sediment from the eroded mountains in the Highlands and deposited it on alluvial fans and along river channels and floodplains. Fans are typically found where a ravine draining from highland terrain emerges onto a flatter plain. As a stream’s gradient decreases and flow speeds reduce, it drops the most coarse-grained material first and the finest grains last. These layers of cobbles and boulders became conglomerates known locally as pudding stones, which have been used extensively in older buildings in the town.

The river-carried sands and muds changed to sandstone and mudstone, with the latter containing primitive vascular plants that have simple roots. The thinly-bedded, finer-grained sandstones, or flagstones, have been used widely in buildings and paving. Thanks to Earth movements associated with the nearby Highland Boundary Fault, most of the strata in the area are turned from horizontal to almost vertical.

In the last 2.5 million years, climate changes have created the current Ice Age. In the last 30,000 years the last glacial period and the current inter-glacial have left a marked impression on the local landscape through deposition of glacial deposits such as eskers and terminal moraines, alongside erosion and deposition features. One small but locally noteworthy feature is the glacial erratic. When the last ice sheet melted about 12,000 years ago, some of the boulders it had transported were dumped on the land surface. These stones are called erratics (strangers) if they are different to the local rocks – one local example is Samson’s Stone – and these can tell us which direction the glacier has come from. The gorges and waterfalls at Bracklinn and Coire Eas na Caillich probably have their origins in erosion caused by major flows of glacial meltwater as ice sheets melted down and retreated from the Callander area. Historic and modern floods continue to modify the landscape.

Text contributed by Mike Browne

Find out more
Mike Browne. 2014. Callander Geodiversity Trail: stories in the landscape. Download from www.edinburghgeolsoc.org/downloads/CCDT_GeodiversityTrail_web.pdf
MAE Browne and C Gillen, Editors. 2015. A Geological Excursion Guide to the Stirling and Perth Area. Edinburgh Geological Society and NMS Enterprises Ltd. Available from www.edinburghgeolsoc.org/publications/geological-excursion-guides/

Split erratic boulder of folded highland metamorphic rock with Samson’s Stone in background. Visit this on the Three Bridges walk. Image: Mike Browne.

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