William Smith and the Birth of the Geological Map

Geological maps are fundamental tools to a geologist. Displaying the distribution of different types and ages of rocks, they are the first step to understanding the geology of a place and key to the search for raw materials. Today, the whole of Britain has been mapped, largely through the work of the official agency, the British Geological Survey. But two hundred years ago, geology was a new science and the Survey was yet to be established. The industrial revolution was in full swing and the demand for coal, iron and limestone was huge. Landowners, keen to find coal on their properties, were being exploited by itinerant surveyors who, through greed and ignorance, persuaded them to fund searches where coal was never likely to be found.

William Smith, a surveyor from Oxfordshire, realised that a map showing where different rock layers - strata - came to the surface would be of value to both landowners and surveyors, not just for locating coal but also for agriculture, showing the different rocks and hence soils of different types. It would take him almost 15 years to complete.

Smith was born on 23 March 1769 in the Cotswold village of Churchill where his father was the blacksmith. He had a limited schooling but at the age of eighteen he was taken on as an apprentice surveyor in the practice of Edward Webb in Stow-on-the-Wold. He showed an aptitude for measurement and mathematics and an eye for the shape of the land. In 1791 Smith was sent to survey and value coal mines in the Somerset coalfield south of Bath, and two years later was appointed to survey the route for a new canal to transport coal from the mines.

Discoveries

During the six years that Smith worked on the Somerset Coal Canal, he made two fundamental discoveries. The canal was to be constructed in two branches in adjacent valleys and Smith noticed that the sequence of rock layers was not only the same in each valley but that the layers were always tilted towards the southeast. During his travels around the country to examine other canal routes, Smith realised that the strata of southern England always occur in a regular order and all were tilted in the same direction. His other discovery was the realisation that certain fossils were associated with particular strata; this meant that he could use the fossils to identify where a layer of rock lay in the sequence of strata.

The practical application of these discoveries was immediately obvious to Smith. Coal occurs in association with grey mudstone rocks, but such rocks appear in several places in the sequence of strata, both far below and above the coal. Using fossils, Smith could identify which grey mudstones were part of the coal beds and which were not, and with his knowledge of the sequence of strata, Smith could construct a map showing where the different rocks were present at the surface and where coal could be found.

When Smith explained his work to his friends Joseph Townsend and Benjamin Richardson in Bath on 11th June 1799, they persuaded him that he needed to publish his discoveries in order to receive credit for them and, possibly, reward. That evening, he dictated the order of the strata to his friends and soon handwritten lists of the sequence of rocks from the coal up to the Chalk were in circulation. Soon afterwards, Smith sketched a map showing the rocks of the Bath area and a small map showing some of the rock outcrops extending across England. In 1801 he published a prospectus of his intended great work on the strata of England and Wales.

Over the course of the next fifteen years, Smith travelled widely across the country, working on commissions as a land surveyor and drainer. As he travelled, he took note of the landscapes and the rocks, gradually accumulating the information he needed for his map.

Publishing the Map

The map was eventually published late in 1815 by John Cary, a leading London mapmaker. A Delineation of the Strata of England and Wales, with part of Scotland was a monumental work. At a scale of five miles to the inch, it was huge, over eight feet tall and six feet wide. It was spectacularly (and expensively) hand-coloured. It sold at prices starting at 5 guineas for the map in fifteen sheets, plus an index map and an accompanying Memoir. But although Smith’s Memoir listed over 400 subscribers to his map, few had paid in advance, and as his map had taken so long to complete, some of his subscribers had died. We do not know how many maps were sold, but it may have been in the order of only about 350.

During the years of its production, Smith continually altered the map as new information about the distribution of the strata became available to him and there are at least five different issues of the map known.

Within five years, Smith’s map was eclipsed by another, in places more detailed, map, the product of the collaborative effort of members of the Geological Society of London under its first President, George Bellas Greenough. And within twenty years of the publication of Smith’s map, detailed geological mapping came within the remit of a new, government-funded Geological Survey of Great Britain.

Smith’s beautifully-coloured map, however, remains an icon of the science of geology and is widely regarded as the first true geological map of any country. It also the more remarkable in that it represents the work of one man, who single-handedly mapped, for the first time, over 175,000 square kilometres of Britain.

Today the map is much sought-after by collectors and commands serious prices (currently there is one for sale in London for over £90,000). The number of copies still extant is currently being researched, but it is likely to be in the order of 150. The Department of Geology (now Natural Sciences) in the National Museum of Wales is in the unique position of holding nine complete or partial copies of the map, more than any other institution in the world, thanks to the foresight of its first Keepers, Frederick J. North, Douglas A. Bassett and Michael G. Bassett. North, in particular, rapidly established the Geology Department’s map and archive collections as one of the most important in the country and this has been built upon by his two successors. The National Museum is the only place in the world where almost all of the different issues of the map can be examined side by side.

A version of the article was published in Earth Heritage.