study confirmed what documentary evidence also relates: that there was a boom in tin production in the 13th century. The earliest written record of tin streaming comes from the 12th century. Open cast By the 15th century, the sources of stream tin were becoming scarce and since the demand for tin was as strong as ever, the direct working of lodes was considered viable despite the greater effort needed in both extraction and refining. "Beamworks" was the name given by the tinners to workings where the lode was followed by digging down from the surface, and the massive gullies that resulted remain prominent features of the moor today. Several of these gullies retain names that include the word beam: Gibby Beam, Willabeam and Scudley Beam, for example. They are also known as "openworks" or "gerts". Another method of surface mining involved digging pits at intervals along the lode – this was known as "lodeback-work". At times these pits were dug in pairs along the back of the lode and the lode followed underground between them. This may have been the precursor to beamworks in a number of locations, but enough lodeback pits survive to indicate that it was a separate technique. The issue that mine managers had to decide was whether it was worth removing the extra overburden to form a gulley in order to be able to mine deeper into the lode. In a similar fashion to streamworking, much use was made of water for the removal of the overburden and gangue. When digging large gullies the overburden, which consisted at least partly of decomposed granite ("growan"), was loosened with picks, and then water was used to wash away the unwanted material instead of manhandling it. Means of collecting, diverting and storing water were always associated with openworks. In some cases when only poor sources of water were available complex systems of reservoirs were built. Underground The Dartmoor tin industry declined in importance during the early 18th century and had fallen to nothing by 1730. This was due to a number of factors, but the most important was likely to be the exhaustion of the easily accessible deposits. It was not until the Industrial Revolution fuelled demand for all metals and also provided the technology to mine them that mining resumed on the moor on any scale. Although underground mining technology had been available for many centuries, it is