Early October, 2015
On a day of slate-grey, copper and bronze, I find myself birling through Glen Tilt from Blair Atholl on a mountain bike. I’m on a little kind of pilgrimage to find the spot which helped one man to turn the geological world of his time on its head.
Birch and rowan trees blast a yellow and red glow into the valley sides, lighting my way like candles all along the river edge. Deer roar, the sound echoing and reverberating off the u-shaped glen as the autumn rut unfolds on the slopes above. The sound is extraordinarily eerie, a sound centuries old, a sound that doesn’t just slot into the landscape but is an inherent part of it. It’s almost as though the hills themselves add emphasis to the rut, enhancing it.
James Hutton, the well-respected ‘father of geology’, visited Glen Tilt in September 1785 – 230 years, almost to the day, before me. He, like me, was searching for something – evidence to support his suspicions about the inner workings of the Earth, and how rocks were created. At the time, ‘Neptunism’ was a prevailing theory for how rocks and minerals were formed – namely through crystallisation in the oceans. Hutton believed that the Earth’s ‘heat engine’, and volcanism, were at the crux of rock and mineral formation. He began searching for places that would back up his theory of ‘Plutonism’.
The southern half of Glen Tilt is composed of Dalradian metamorphic rocks dating from the Ordovician period (around 485 to 443 million years ago). These rocks were formed when parts of Scotland lay submerged under the Iapetus Ocean, south of the equator. As I ride alongside the River Tilt the water helps show off the bedrock in all its glory – silver-shot rock layers tilt up at an angle, like pages in a book with the spine pressed down horizontal. The birch trees scatter the dark slabs of rock with leaves, like gold coins strewn across table tops.
Further north, the rock compositions begin to change, and not unnoticeably, even to someone who has never studied geology. A stream-cut rift in the valley side reveals pink, crystalline rock – granite. Glen Tilt holds clues to its make-up stemming from the Caledonian Orogeny, a series of mountain-building phases which took place in Northern Europe as the Iapetus Ocean closed and the continents of Laurentia, Avalonia and Baltica collided. The granite in Glen Tilt formed during one of the magmatic periods that occurred in the creation of the Highlands. When Hutton was alive, the common belief was that granite was the original ‘primeval’ rock layer – that it underlay everything and that all other rocks on top of it were younger. Hutton suspected otherwise and at Glen Tilt, he reasoned, somewhere the two types of rock had to meet. This is what he was looking for.
I’m still searching. Around eight miles from the Glen Tilt carpark is Forest Lodge, a large sporting lodge run by Atholl Estates. I know that Hutton’s spot, his ‘eureka moment’ if you like, is close by, but I didn’t anticipate quite what I would find there. As I come out of the well-managed copse of trees surrounding the lodge I meet a curve in the river, two deep pools created in amongst otherwise tumbling rapids. The river sides are bare rock, and I’m standing about 15 feet above the water. This is the place where two rock types met, and meld, and twist together in patterns not unlike marbled paper. Grey meets red meets pink.
Two huge salmon – two feet long – leap in the pools below my feet. I’m standing where Hutton once stood, at the same time of year. The fish slam their bodies up against the current, their tails whipping the air before they smack back down into the river. Hutton, on his visit here in his quest for evidence for his ‘Theory of the Earth’, made the same seemingly effortless leaps against the prevailing currents of thought at the time. He transformed the Earth from solid mass to a dynamic, fluid and ancient system driven by heat; a perpetual recycler of rocks and minerals – and, above all, a product of deep time.
For Hutton realised, in this spot, that the granite was younger than the metamorphic bedrock. He understood that the only way the two rocks could have part-mixed together was if one of them was molten at the time. The granite had to have been injected into weaknesses in the Dalradian rocks. I’m standing here, on my own, having not seen a soul since leaving Blair Atholl, and I get it. That kick of sheer satisfaction. That moment where everything falls into place – the split second where everything just fits.
The tinest hint of a breeze. The candle trees flicker. The river ploughs onward, shaping the beautifully-patterned rocks into swirls and curls that echo the eddies in the water. There are a few places where I’m there just long enough to leave a piece of my heart and soul behind. This is one of them. Glen Tilt. Hutton’s breakthrough and a fleeting glimpse of the power of our planet, immortalised in stone.
All text and photographs are copyright L. Reid 2015
My thanks to Angus Miller for the fact-checking, proof-reading and positive encouragement over the last wee while!