With my interest in all things geological, and maps in particular, sparked by Garry Hogg’s idea of following the oolitic limestone across England, I remembered that amongst my legions of as yet unread books I had a copy of Simon Winchester’s biography of William Smith – ‘The Map That Changed The World’.
Smith – ‘the father of geology’ – produced what is widely accepted to be the world’s first geological maps. Most notably this map of England and Wales, published in 1815.
The oolitic limestone, it transpires, was important to ‘Strata’ Smith – he grew up in Oxfordshire, on the oolite, and his interest in geology began with the fossils he found there as a boy. As a young surveyor he moved to work in the Somerset coal-fields, and to plan a canal to link those coal mines with Bristol. Travelling down mine-shafts and cutting the canal gave him an insight into the complex ways the strata, including oolitic limestone, were folded together in that area. Later he lived in Bath where the iconic buildings are clad in oolitic limestone and the hills to the east of the city are of the same rock.
In the middle of ‘The Map That Changed The World’, Winchester breaks off from telling the story of Smith’s life and discoveries to recount his own journey along the limestone, starting, like Hogg did, at Burton Bradstock.
Small wonder that William Smith found the area around Bath the most congenial for his studies. Not only was it an attractive town, jammed with interesting personalities and lively minds; it was also happily sited at a place in the country’s immense geological mosaic in which the Middle Jurassic rocks outcrop in a blindingly obvious way. The general line of their outcrop, which extends all the way north from Dorset to the Humber in Yorkshire, some 200 miles, is one of the great dividing lines of world geology, once seen, never forgotten. Around Bath, close to where a northbound traveller like me today, Smith two centuries before, first comes across it, it is stupendously memorable.
On the western side of the line are the timid, milquetoast Clays and weakling Shales of the Lias, of the lower Jurassic; on the eastern side are the tough, thick Oolitic Limestones of the Middle Jurassic. On the western side the consequential scenery all is valley and marsh, river course and water meadow, lowing cattle and in high summer, a sticky, sultry heat; on the eastern side, underpinned by the Limestone, everything has changed – there is upland plain and moor, high hills, high wind and flocks of sheep, and in the winters fine white snows blowing on what can seem an endless and treeless expanse.
And on the very line itself, at the point where England has tipped herself up gracefully to expose the Limestones at her core and to reveal the huge physical contrast between their hardness and the silky softness of the Lias Clays below, is a long, high range of hills and cliffs. This line is, for the most part, an escarpment edge that rolls far to the horizon, separating vales and downlands from high plains and uplands.
We see this line in scores of places. Down at the southern end of the country – the Bath end – we see it where Crickley Hill and Birdlip Hill rise hundreds of feet above the town of Cheltenham. We see it where Wooton-under-Edge (a village set on Lias Clay) nestles below the village of Oldbury-on-the-Hill (on Middle Jurassic Limestone). We notice, we feel it, when we drop sharply down from it via a dangerously twisting switchback road as we descend westward from the high plains of Snowshill (on the Middle Jurassic) to the antique shops of the clay-valley town Broadway (on the Lower). We can see it unroll over a dozen miles if we drive along the traffic-clogged roadway of the A46, on the stretch between Bath and Stroud: on going north, everything visible to the left is Lower Jurassic Clay, and hunches low to the horizon; everything to the right is Middle Jurassic Limestone and rises high, its edge topped with oaks from which big black crows take in the view of the grassy fields below.
We see the phenomenon exhibit itself over and over as we rumble northwards across the land – we see it through central Gloucestershire and Warwickshire, through Rutland and Leicestershire, across Nottingham and Lincolnshire – such that when, a day or two after I had left the warmth of Dorset, I found myself in the cold of Lincolnshire coasting along the A15 northbound from Lincoln (where there stands a fine Jurassic cathedral, made of just the same age limestone as that at Wells, down at the far southern end of the outcrop) to Scunthorpe, almost exactly the same held true. To my right rose high limestone plains, buffeted by North Sea winds, dotted with sheep, flat enough and suitably exposed for the building of great Air Force runways and training schools and hangars, To my left, lay a long low valley, thick with farms, populated and cosy. The Middle Jurassic formed the upland landscape to my right; the Lower Jurassic the lowlands to my left.
Better and better. A walker following the western edge of that ‘buttercup-yellow line’ would be teetering along an escarpment edge. High drama!
Now I know the A15 from Lincoln north to Scunthorpe well. I drive it quite often on the way to and from my parent’s house – they live about a mile from that road and from RAF Scampton where the Red Arrows practise. You may feel sceptical about Lincolnshire’s ‘high limestone plains’ and perhaps this should be taken with a sizeable pinch of salt – but I do recognise the description, up to a point. The A15 is another Roman road – Ermine Street – arrow straight. Sensibly it follows a ridge of higher ground (about 60m above sea level so not that high!) ; to the east the land falls away gently but a little way to the west is the Lincoln Edge – two or three closely parallel contours dropping down to a valley which, on the Landranger map, has many adjacent grid squares completely devoid of any contours. Lincoln itself sits on the edge, the Castle and Cathedral atop the edge and the more touristy shopping streets dropping down to newer parts of the city below.
Walking the Lincoln Edge would mainly involve walking along a B-road so perhaps not ideal. But I must admit that Hogg’s idea has certainly kept me happily occupied in spare moments whilst my dodgy ankle, now thankfully on the mend, has precluded the making of more immediate concrete plans.