Llechwedd Slate Caverns

History and Archeology

Slate has been used for roofing since the Romans discovered its qualities and used it at their fort at Segontium - today known as Caernarfon. They also used carved dressed pieces for wall hangings. The earliest Welsh use of roofing slates was in the 12th century at a site that appears to have been fortified by Owain Gwynedd, Prince of North Wales. King Edward 1st architect certainly used slates to roof Conway Castle. Slate really started to be used in commercial quantities during the industrial revolution for roofing the vast numbers of new houses that were being built all across the country. Then it was exported around the world. Welsh slate was a quality product.

The Llechwedd complex of slate mines was central to this production of slate. It comprises several workings that were historically known as separate entities such as Diffwys, Bowydd, Maenofferen as well as Llechwedd its self. Slate was worked here at Diffws (1 mile east of the Llechwedd tourist complex) in 1775 but the others started on the 19th century. Blaenau Ffestiniog's slate remained hidden for a long time because the 30º angle of the beds left them only outcropping in patches; elsewhere the beds are near vertical or horizontal. This meant that the slates had to be mined until the recent modern machinery allowed open cast operations.

Enormous caverns were carved out underground, a process that was made possible through layers of igneous rocks that provided secure roofs. Eventually there were 16 floors at Llechwedd all identified in relation to the point at where the slate was found in 1849. This became known as floor 1 and the subsequent floors were numbered upwards (1-7) and downwards (A-I) giving a vertical distance of about 305 metres underground. Tracks were laid to help move out the great blocks of slate to the surface and to the surface where they were trimmed and split. Professional slate workers can produce great numbers of slate from the slabs using a chisel. It is commonplace for splitters to produce about 35 sheets per inch and at the London Exhibition of 1862 the founder of Llechwedd, John Greaves, won a medal with slabs 10ft long and 1 ft wide but only 1/16 of an inch thick.

The slates had to be transported to the coast where they were shipped around the country and overseas. At first this was done by hauling them down the toll road to the quays at Tanybwlch. But the erection of a land reclamation embankment across the mouth of the River Glaslyn in 1813 scoured a navigable channel across the Dwyryd estuary. This soon led to the creation of Port Madoc and in 1836 a narrow gauge railway, the Ffestiniog Railway, opened up to link the harbour with Blaunau Ffestiniog. 1851 the office was moved from Llechwedd to new wharfs in the harbour. About 260 ships were built at Port Madoc with most of constructed to carry slate to the new markets opening up everywhere. In 1869 the Cambrian Railway came to Minffordd enabling slate to be reloaded to standard gauge stock and taken by train to the major cities. The London and North Western Railway cut through from the Conwy Valley in 1879 providing Deganwy as an alternative harbour. Finally the Bala and Ffestiniog Railway, later part of the Great Western Railway, arrived at the town.

New skills were needed to speed slate production and the owner, J.W.Greaves, was at the forefront of innovation. He devised his own sawing table and a slate-dressing engine that is still used whenever slates need trimming for roofing. This high technology of its era, the railway and the new harbour made 1850 the turning point for Greaves and Llechwedd. In this year 1,128 tons of finished roofing slates, with a value of £2,114, were sold, putting Llechwedd on a level with the big producers.

Hydro-electric generation was installed at Llechwedd in 1890 and in 1904 this was improved by harnessing the power from two lakes above the quarry. They remain in use, occasionally feeding power into the national grid.