Over a period of about 150 years up until the 1920s, the open valley of the River Tawe became one of the most heavily industrialised areas of the developed world. There were a number of reasons that favoured the great expansion of industry in this particular location. The general exploitation of coal in the South Wales coalfield of the South Wales valleys had revealed seams of steam coal and anthracite close to the surface in the Upper Swansea valley and these were easily exploited by shallow drift mining or open cast mining. Smelting metals required more than three parts of coal to every one part of metal ore, so it was of major economic benefit to have easily available, high quality coal. Swansea also had a good port and safe anchorage. The combination of these two factors meant that it was financially more viable to bring the ore to Swansea's coal than take the coal to the ore. In addition, the very high tidal ranges at Swansea allowed deep draught ships to access the river mouth. This allowed large quantities of raw materials to be brought in (allowing further profit through economies of scale) and, more importantly, the finished products, such as sheet copper, tinplate, alum, porcelain and coal to be exported.