Around 1824 a coal seam called Waun Wyllt (or Abercanaid Level), a few miles down the Taff Valley from Merthyr Tydfil was opened by Robert and Lucy Thomas, who came from west Wales. Robert took a on a yearly tenancy from the Earl of Plymouth. The Roberts became the first to mine the 4 feet seam of steam coal with which they supplied the householders of Merthyr and Cardiff. A short tramway was built from Thomas's Level to the Glamorgan Canal which was the main transport route up and down the valley.
After the death of Robert, his widow, Lucy, and his son William took over the family business. They, through their agent George Insole, shipped a cargo of their coal to London, where the smokeless and steam rising quality of the coal soon led to a contract to supply Messrs. Wood and Company, London coal merchants, with three thousand tons a year.
Lucy Thomas moved from the Waunwyllt level in the mid 1830s when the yearly tenancy was terminated, and leased the neighbouring Graig property, which was a pit 60 yards deep. A visitor to her Craig Pit gave this description of Lucy Thomas in 1840.
"She sat in her office, a hut near the pit's mouth and traded for cash, placing in a basket over her head, the monies she received for the coal".
From a list 1869 the owners of Waunwyllt were Graig Coal Co., It closed in 1870.
Because of her part in this venture Lucy Thomas (1781-1847) became known as "the mother of Welsh steam coal trade", and the activities of the Thomas family marked a new episode in the visual and botanical transformation if the lower South Wales valleys and their uplands which continues still as the pithead sites and spoil heaps are reshaped for the accommodation of new businesses.