Walking the Corbetts Vol 2 North of the Great Glen. Brian Johnson
over 200 million years was followed by uplift and tilting downwards to the west. By 540 million years ago, erosion had formed a near-horizontal surface.
Moine schists: At the same time as the Torridonian sandstone was being laid down in the west, silt was being laid down in the east. The silt was pushed down into the earth’s crust and passed through a series of metamorphic processes, with the individual mineral grains in the schist being drawn out into flaky scales by heat and pressure, with the result that the schist splits easily into flakes or slabs. The gentler mountains in the north-east of Scotland are mainly composed of these Moine schists.
Basal quartzite 570–550 million years old
Basal quartzite, pipe rock, fucoid beds, Salterella grit and Durness limestone: Eventually, after a long period of erosion, the remains of the Torridonian sandstone in this part of Laurentia sank beneath a shallow sea. A thin sequence of sandstones, siltstones and limestones were formed in the coastal sand-bars, tidal flats and in the sea. Clean quartz sand was deposited on top of the Torridonian sandstone and a pure sandstone composed of rounded grains of quartz, cemented by further quartz between the grains was formed. This sandstone had completely different properties and is the rock we now know as basal quartzite, a white rock which is resistant to weathering and erosion. Life was developing in these waters and there is a layer of quartzite called ‘pipe rock’ where there are pipe-like burrows of fossil worms. As animals with shells developed, their fossilised remains resulted in the sediments becoming richer in ‘lime’ and in the formation of the Durness limestone.
The remarkable thing about these rocks is that the fossils are identical to those found in the Appalachian Mountains in the US but distinct from those of the same age in the rest of Britain. It is now clear that 500 million years ago Scotland, Scandinavia, Greenland and north-east America were one continent and that they were on the opposite sides of a now vanished Lapetus Ocean to the rest of Europe. This was the first conclusive evidence for continental drift.
About 430 million years ago there were intrusions of magma creating sills of crystalline rock parallel to the bedding plane, dykes cutting the bedding plane as well as plutons (irregular masses).
Between 430 and 420 million years ago a vast mountain range was being built up to the south-east as the Lapetus Ocean had closed and the ‘European plate’ was moving north-west and colliding with Laurentia. The most dramatic effect on Scotland was the pushing of a large slab of the old Moine schists over the younger rocks of north-west Scotland. This is known as the Moine Thrust.
Eventually, Scotland collided with England and fused to form one land mass before quiet conditions returned. There is no evidence in the rock record of any activity in north-west Scotland but this was a period of the build-up of sediment forming sandstone, coal, limestone, chalk and other sedimentary rocks in the remainder of Britain.
Around 60 million years ago the continent split apart, with Europe and Africa separating from America, as the Atlantic Ocean began to develop and there was volcanic activity along Scotland’s western edge.
Glacial moraine hummocks in Choire a’ Cheud-Chnoic, Torridon (Route 59)
During this time the climate cooled and by 2 million years ago the Ice Age began to affect the whole planet. Scotland would have been buried under ice and would have looked like Greenland today. It was during this time that today’s landscape developed, with massive glaciers carving out the U-shaped valleys which are such a feature of the Highlands today. Glaciers would also have carved out the corries and transported boulders long distances to scatter them over the landscape.
As in Greenland, the highest peaks would have stuck out of the ice and so wouldn’t have been smoothed by the ice, but left jagged and angular. The white cap of resistant quartzite on many of the Torridonian sandstone peaks would have helped protect them from erosion, leaving the spectacular peaks we see today. As the glaciers and icefields melted there would have been enormous flows of meltwater flowing beneath and out of the glaciers, cutting out gullies and gorges.
It wasn’t until about 11,000 years ago that the last of the glaciers finally left Scotland and peat bogs began to build up in the warmer wet conditions. Peat forms when plant material is inhibited from decaying fully by acidic and anaerobic conditions, usually in marshy areas. Peat bogs grow only at the rate of about 1mm per year.
For more information see www.scottishgeology.com or www.northwest-highlands-geopark.org.uk.
Walking the Corbetts
Walkers on the 801m subsidiary summit of Baosbheinn (Route 63)
The walks in this guide have not been designed for the peak-bagger, but primarily for the walker who wants an interesting day out on some of the less well-known but most spectacular peaks in Scotland.
Some people think the Corbetts are something to do in your declining years after you have ‘compleated’ the Munros. If you take this attitude you will miss out on many of the most spectacular and rewarding mountains in Scotland. It is true that as you get older you may appreciate the shorter walks offered by some of the Corbetts, but many of the Corbetts are very remote from road access and will still give a demanding hike. What is more, between many of the peaks listed as Munros, there is little drop, so you can often climb several in one day. By contrast, the requirement for a 500ft drop on all sides between listed Corbetts means that there are few occasions where Corbetts can be linked together. It is also surprising how few Corbetts can sensibly be combined with climbing a Munro.
This two-volume guide suggests 185 day-hikes to climb the 221 Corbetts. All the routes were walked by the author when preparing this guide. Suggestions are also made for alternative routes, but these have not always been checked by the author. This volume covers 109 Corbetts in 90 routes.
There are some areas, such as Knoydart, where the Corbetts are so remote that walking them in a day will be too much for the average walker and backpacking possibilities are considered.
When to Go
Gleann Chorainn, Bac an Eich, Strathconon (Route 49)
You will find people hiking in the Scottish Highlands throughout the year but this guidebook assumes that the Corbetts are being walked when they are free of snow. The mountains can be at their best in the winter, but weather and snow and ice conditions mean this won’t be the time for the inexperienced walker. For the experienced walker, winter in the Scottish Highlands can be magnificent. In the middle of winter there will be less than eight hours of daylight and climbing Corbetts could be a better option than climbing the Munros.
The spring in Scotland is often drier and sunnier than the summer and many consider April and May to be the best months for being in the Highlands. June, July and August are the warmest months, with the added advantage of the long daylight hours. The biggest problem with the Scottish Highlands in summer are the swarms of midges that can torment the walker, especially in the early morning and on still evenings. This is not too much of a problem for the day-hiker, but it means that this isn’t the ideal time of year for backpacking and wilderness camping.
September and October are generally relatively dry and you won’t have too much problem with midges. A combination of autumn storms and short daylight in November and December means that you are likely to be on your own in the mountains.
The Terrain
Many newcomers to Scotland underestimate the conditions they will encounter when walking in the Scottish mountains. The mountains in this guidebook may be under 1000m high, but you will usually be starting your walk from near sea level and you will spend