Bilston Burn and the geology of the Lothian coal field

Our Treasurer, Rennie Frazer, wrote this item whilst ill in hospital in 2021. Tragically he died shortly afterwards from Covid.

“My geography teacher at Portobello High School was Mr Baggaley. He was an enthusiastic exponent of the post glacial landscape of Scotland, an enthusiasm which has remained with me ever since. Solid geology was another enthusiasm, but in this case his Yorkshire origins blinded him to the respectable outcrops of Millstone Grit on the Joppa Shore, a ten-minute bus ride from the school. Instead, we were given descriptions of the Great Pennine escarpments capped by this stone.

I was recalling his lessons as I listened to an Esk Valley Trust talk on the problems caused on the South Esk by the flooding of the abandoned Bilston Glen Mine.

One of the striking aspects of the talk was the complexity of the underground geological and mining architecture, which resulted in waste water from the flooded mine emerging close to the South Esk, many miles from the mine and taking a subterranean route below the nearby North Esk.

The geological map of Edinburgh and Midlothian dates back to 1859. The map is a multi-layered plane surface, on which the coloured blocks of rock types are the most prominent feature. But the map is based on Ordnance Survey cartography, with much of that information also visible in faint print. Further geological features such as faults and strata dips are shown by symbols, so that a three-dimensional image of the structure underlying the surface landscape emerges. Where the imagination fails cross sections illustrate the continuity of bedrock strata below the surface. One cross-section follows a zig-zag path which takes in all the major geological features of Edinburgh; the Castle Rock, the volcanic vents of Arthur’s Seat, followed by a right angle turn to traverse the Lothian Coal Measures. The key to rock types is arranged by geological era, so that the map achieves the incredible feat of mapping in both three space dimensions and a fourth time dimension.

The Coal Measures were charted by detailed field work over more than a century, with outcrops along the Bilston Burn being the source of empirical data on the sequence of sediments comprising the western outcrops of the Lothian Coalfields. This sequence has been lost since the sinking of the Bilston Glen mine in the 1950’s as the waste from the mine buried the burn which is now confined to an underground culvert. Objections to the loss of a valuable scientific resource were raised in a parliamentary debate in 1952 and in minutes by scientific societies.

The National Coal Board had considered constructing an aerial ropeway from the mine to the Hewan Bog to deposit the waste there. This proposal was not followed because of the costs of construction and of acquiring the land. Had Bilston Glen continued in operation for a century, as was originally planned, then the Hewan Bog, nevertheless might have been required to accommodate the waste – but the disposal of waste over the Bilston Burn would still have obliterated an important historical source of geological information.

This significance of this loss can perhaps be gauged by the following report from the Scotsman, when the Bilston Burn excursion was both a worthwhile field trip and a local natural beauty spot.

The Scotsman; Edinburgh, Scotland, 19 Apr 1915: page 6

Members of the Edinburgh Field Naturalists’ and Microscopical Society had an excursion on Saturday to Bilston Burn, under the leadership of Mr T. Cuthbert Day. The members of the Society studied the fine sections through the lower limestone series of the carboniferous so well exposed in Bilston Burn. Particular attention was paid to the various bands of limestone, and the evidence correlating these limestones and other beds with a corresponding series between Kinghorn and Kirkcaldy on the other side of the Firth of Forth.

The loss of information at this site is readily evident today – just take a look at your OS map for the area just east of Dryden Tower (NT 275645).

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