A map of 1833 showed Thanet Street and Clay Lane. The railway 'mania' of 1840s witnessed expansion northwards facilitated by the Clay Cross tunnel dug in 1837–38. Whilst tunnelling over a mile underground they discovered vast quantities of commercial grade coal. Clay Cross became a boom town. The 'Liverpool Party' of Stephenson engineers formed the Clay Cross Company in 1839 which they funded from their considerable resources. As well as sinking a number of shafts with colliery support, there were coke oven works, brickworks, limeworks, irons furnaces and foundry. The ductile pipe was developed into an internationally sold product, making Clay Cross renowned for its iron and coal industry worldwide. Although the company had been formed to mine coal and manufacture coke from the railway, the supplies from Durham were preferred, and the works turned to iron working and brick making. When Stephenson died in 1848 his son, Robert, took over, leaving the company in 1852 when it became formally known by the name of the Clay Cross Company. In 1871 the Jackson family acquired 100% of the stocks and shares. They continued as owners until 1974. For many years, the company was the town's major employer. In 1985 Biwater took it over. In December 2000 Biwater sold the site to French company, Saint-Gobain. Some months later, it was closed down with the loss of around 750 jobs. Demolition of the vast Biwater site began in late 2008, and new houses and shops are appearing in the town.