The standard gauge line there was routed to Narberth and also Saundersfoot to meet the needs of the mines and quarries etc. It was very different from the South Wales Railway Company's approach on the main line with Brunel wanting a direct link with Ireland but not interested in linking up towns, villages or industry. (For those who may not know, it was not the Great Western Railway who built the line into South Wales, but Brunel (Junior) did have involvement in it. The Great Western Railway took over ownership at a later date... The SWR had a gauge of 7'0"). What I'm not sure about, was when the date the GWR took over from the SWR, as it could be part of the line further west was completed in GWR hands.
The old Saundersfoot tramway (To differ it from the Pembroke and Tenby Railway) had stone sleepers which parts are still in place. The coal indeed does come to the surface at the sea edge, and it was due to this reason that the coal was "Mined". The coal seams further west were also thin but of top quality. One of the early areas to mine coal was the Gwendraeth Valley mining into the side of Pembrey Mountain. The valley used to have a very large wood which stretched all the way up the valley floor but this was removed during the early days of the industrial revolution as a fuel source for the hungry furnaces (E.g. at Furnace, Burry Port which used to all be in the Pembrey parish prior to the industrial revolution). When the forestry was almost completely removed they had to then look for other fuels, so by the 1700's came along, they had already turned to coal mining.
The early mines in the side of Pembrey Mountain were known as " Cell Mines", as back in those days they just dug in a short distance, removed the coal, and then started another "Cell" and so on. They didnt have pumps or fans for ventilation in those days.
They took the coal in saddlebags on the backs of donkeys to the inlet on the east side of Burry Port, where today they have the sand dredger parked up.
The next stage of technology came in three ways. First new mines were built using water adits to drain the water. One example was Stanley's Pit, where an embankment with a tramway took coal to the newly dug Pembrey Harbour. Today only the outer bay exists. Around the same time a few canal systems were being built to link both the mines in the Gwendraeth Valley with the sea, notably the new Pembrey Harbour and the ancient Kidwelly Harbour. Due to regular silting up of the harbour at Pembrey, (It had used Swan Pool as a means to flush it out but it wasn't successful. The Swan Pools in Pembrey were also used to supply water to the canal systems. The Swan pools were later totally drained via a dyke system known as Swan Pool Drain after the canals were abandoned. Much of "The Links" was built on top of this reclaimed area. The Stanley's Pit adit went right under the new houses that were built on the marsh east of Pembrey church, and most of the later houses in Danlan road (Seaward side) before it headed towards the sea. The adit constructed can't have been cheap as it is made from Victorian brickwork in an arched form.
Railways then came along, and the old canals were mostly abandoned. One railway was built partly on top of one of the old canals and was known as the Burry Port and Gwendreath Railway. Notice the spelling mistake which was made when the company was registered in parliament!
Later came the invention of steam pumps so adits were no longer needed to drain mines.
The canal that went up the valley was interesting. In order to address the gradients, rather then use lochs, they had two slide type devices that had rollers. They were basically shoots with rollers where the flat bottomed canal boats could be slid up or down. By the nature of the industry, the heavy full barges would be in the downward direction so gravity could assist.
The railway built on top of this canal often used to flood and even put out the fires in the locos! I remember watching triple headed class 03's ploughing through the flooded line on a daily bases!