Aberthaw's maritime trade continued throughout the 18th century, but by the 1840s, its role as a port declined: the harbour 'is resorted to by a few coasting-vessels of inferior burthen', as the "Topographical Dictionary of Wales" in 1849 reported. In 1851, Aberthaw had a population of 495 people. The principal material then being exported, however, was the local lias limestone, called Aberthaw tarras, which was used to make hydraulic lime, which sets under water and was therefore very useful for building light houses (including the Eddystone Lighthouse) and canal locks. This limestone, considered to be of high quality, was to play a key role in the local economy during the ensuing years, beginning with the opening of Aberthaw Lime Works in January 1888. From December 1897, the area was served by the newly constructed Vale of Glamorgan Railway, and a second plant, the Aberthaw and Bristol Channel Portland Cement Works, began production to the north of the village in 1916. Today, the Vale of Glamorgan line remains open. This provides a link to the power station and cement works, and after being closed to passengers on 13 June 1964, was reopened to passenger traffic on 10 June 2005 but only with Rhoose (for Cardiff International Airport) and Llantwit Major stations rebuilt.