A geotourist at the Rock and Spindle

Back in May I was up in St Andrews for a meeting, and as the weather looked promising I took my camera and an early train and set off to spend a couple of hours touristing beforehand. My destination was a volcanic formation known as the Rock and Spindle, a kilometre or two east from the town, which I’d wanted to see since being told it was a classic refutation of the convection theory of columnar jointing.

It was one of those days when you can be unashamedly glad to live in Scotland: sharp sunlight, but there was a fairly snell wind setting in from the east, driving waves two or three metres high and with gulls slaloming on it. The gorse was blazing, and and down by the shore the occasional oystercatcher was plaintively asking “how many?” in Gaelic: “Cia mheud? Cia mheud?”

The route, part of the Fife coastal path, leaves St Andrews via the East Sands before climbing up and running along the top of the cliffs. There are some good views back to St Andrews which illustrate how the ancient part of the town sits on a platform of sandstone, since reinforced by chunks of defensive wall.

Looking back to St Andrews.

Looking back to St Andrews.

It’s hard to look at it without recalling an image of a very different holy place, the Highlandman in George Mackay Brown’s Culloden: The Last Battle “praying to every crossed and beaded saint / That swung Iona, like the keel of Scotland, / Into the wrecking European wave”. If Iona is the keel, then St Andrews is surely the prow that Knox swung into the same still-breaking wave…

From the path there are also frequent sights of the rocky foreshore below. This is classic Midland Valley Carboniferous geology, with alternating beds of siltstone and mudstone (the Sandy Craig and Pittenweem formations, and perhaps a corner of the Anstruther formation, according to the useful BGS online map), differentially weathered and also buckled into several large synclines and anticlines. Even to a casual eye, the dip of the beds changes two or three times in the course of the walk, and there are some fairly unmissable features like this one.

Eroded syncline, just beyond the east end of East Sands.

Eroded syncline, just beyond the east end of East Sands.

Eventually the path drops to the beach, rounds a small point, and abruptly leaves you in a very different geological environment, described unexcitingly as the Scottish Late Carboniferous to Early Permian Plugs and Vents Suite. The name does no justice to this remarkably dramatic change of geology: instead of the sedimentary layers, suddenly everything is dominated by dark volcanic tuff, mostly fine but with scattered angular clasts as well as regions where it’s later fractured and been invaded by water, leaving hair-fine nets of quartz veins against the black.

Basically the rock here is a right mess, and it is easy to believe that it’s the result of a volcanic intrusion shattering its way through the older sedimentary material and leaving a mangled band around its outskirts. The intrusion is, in fact, very localised: it’s confined to a pocket just a couple of hundred metres wide, within which three stacks muscle their way out of the sand.

Looking down on the Rock and Spindle (L) and another stack. Note the eroded dome apparent in the rocks beyond the beach.

Looking down on the Rock and Spindle (R) and another stack of volcanic tuff (L), with near-vertical bedding.

The south-eastern stack is the Rock and Spindle, and it’s quite a remarkable object. Essentially it’s the remains of part of a volcanic vent system, which seems to have forced its way through an earlier pyroclastic deposit. One part of the vent system extends vertically to form the Rock, and this is an agglomerate containing not just the intruding magma but anything else that fell into the vent and got mixed up with it. The other part of the system consists of basanite, a roughly horizontal cylinder of extruded magma which has been truncated to form the Spindle. What’s remarkable about the Spindle is that as the basanite cooled, it formed columnar jointing — not in the usual pattern familiar from Staffa or the Giant’s Causeway when cooling takes place from the top down, but in an approximately radial pattern that reflects cooling from the outside in. The effect is of a gigantic fractured wheel, or a wrecked rose window, nearly four metres across.

The Spindle, with the Rock in the background. Walking stick is 90cm long.

The Spindle, with the Rock in the background. Walking stick (propped against the base) is 90 cm long.

Columnar jointing on the Spindle, seen from the landward side. Hand lens (visible below the plant) is about 2 cm long.

Columnar jointing on the Spindle, seen from the landward side. Hand lens (visible below the plant) is about 2 cm long.

The contact between basanite (above) and tuff (below) on the seaward side of the Spindle. Note the quartz veins and xenoliths in the tuff.

The contact between basanite (above) and tuff (below) on the seaward side of the Spindle. Note the quartz veins and xenoliths in the tuff. Hand lens is about 1 cm across.

Apart from this vivid illustration of jointing, the formation is a lovely place for the amateur geologist to poke around because of the sharp contrasts between one component and another. The contact between the intrusion and the underlying tuff, shown above, is particularly well defined — it’s one of those rocks that seems to tell its own story with only a little questioning.

Which, I admit, is a fallacy. One of the tenets of the Reformers, still a key doctrine for many Evangelicals today, was the “principle of perspicuity” which understands the true sense of scripture to be clear to any reader — or at least, in a useful get-out clause, to any reader whose vision is not impaired by sin. There’s some irony in the way that some modern presentations of science have co-opted this principle as applied to the “book of nature: shown the evidence, only the sinful — or the extremely dim — could fail to realise that etc. etc. (I don’t know who first employed this rhetorical manoeuvre, but I can readily believe it was one of Galileo’s dirty tricks.) In the case of geology, if we’re not careful we end up telling a kind of Jacob’s-pillow story about sites like this: head meets rock in a holy place, and revelation bursts upon us as it did on, say, Hutton at Siccar Point

In reality, the effect of head meeting rock is more usually that the rock wins than that the head does. I’m sympathetic, as it happens, to holy places, but they aren’t generally sites of simple revelation. On a pilgrimage, even a short one, you bring your wisdom and your foolishness and your niggling questions and your ways of reading what you experience; and the point of the journey, as of any honest enquiry, is not to abandon these (as if you could) but to plumb them and pass through them. So, in any case, I crawled over the Rock and Spindle for about half an hour, trying to build a story and failing to notice dozens of details I read about later, before remembering that a proper geologist would have asked a few more questions by this stage about the general context.

At the top of the beach behind the Rock and Spindle one can find more tuff, with a few xenoliths as well as those invasive fractures. Then, only a few tens of metres beyond this monument to destruction and devastation, you reach the edge of the intrusion and suddenly you’re back among thin-bedded silt- and mudstones, layered like patisserie and reflecting — so we read them — the hundred-thousand-year incursion and excursion of shallow seas and swamps across this disputed patch of coastline.

Thin-bedded sedimentary rocks (silt and mudstone?) at the top of the beach just east of the Rock and Spindle.

Thin-bedded sedimentary rocks (silt and mudstone?) at the top of the beach just east of the Rock and Spindle.

I tried to find the limit of the volcanics but lost it amid the scrubby grass and the usual trash of the high-water mark: the usual tangle of rope, creels and cuttlebones, and the skeletonised corpses of two puffins, victims of the spring wreck, both still wearing the remains of their brightly-coloured courting bills.

1030157-croppedEventually, feeling time catching up with me, I turned myself back in the direction of the town. It may have been my brain hunting for a tenuous conceit, but the tower that juts out of the west end of the cathedral nave like a mediaeval Dan Dare rocket did seem to echo the Rock and Spindle’s vertical vent, and either site would have been slightly too easy to tell a simple story about…

There’s a postscript, of course. As I made my way back through town, I stopped by the visitor centre to ask them whether they had any information about the local geology. The staff were willing but puzzled. Geology? No, but they had a leaflet about genealogy if that would help. Evidently not everybody shares my priorities as a tourist.

Further reading. There’s an excellent wee guide on the Geowalks site, pitched for Higher Geology, but at a level that’s easily enough to keep me satisfied. If anyone can refine or contradict anything written above, please let me know…

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