Dorothea Quarry dates back to about 1820 and was to become one of the
biggest slate quarries in Snowdonia. The quarry is in the form of a pit
working in the bottom of the Nantlle Valley. During the 19th century, the
quarry used a whole string of different pumping systems.

Around 1900, the owners started work on a pumping scheme. This involved
digging a vertical shaft that went down below the then bottom of the quarry.
The final depth of the shaft was 122 yards, but the quarry ended up slightly
below this, and needed an additional pump.

To do the main pumping to the surface a Cornish engine was built. It was
built by Holman Brothers of Camborne and was designed by Nicholas Trestrail.
It started work in 1906 and ran through to about 1956 when electric pumps
were installed. It is thought to be the last but one Cornish engines built
and the most modern in Britain outside Cornwall. The cylinder has a diameter
of 68" and a 10ft stroke. The boilers came from "Messes Radcliffe & Son" and
are thought to be second hand from cotton mill.

The restoration firm of 'Dorothea Restorations' gets its name from the
engine, as the group was established to start the restoration process. They
were able to operate the engine around 1970, using a very big compressor and
wheel barrow wheels in place of the valves (that had been removed and 'lost'
some time before). The engine currently looks rather 'sad' as when the pump
rods were cut, the engine was allowed to go 'in house' leaving the cut off
end of the rod out of the shaft.

Grant money has already been obtained for, and spent on, removing the
asbestos insulation from around the cylinder. Partially because of the ivy
that has grown up the outside, the building is in need of repointing. The
question of whether the beam is cast iron or cast steel leads to the thought
that if it is cast steel, it need to be protected from the weather (paint or
'waxoil' type waterproofing).

The quarry ceased production in 1970 and was allowed to flood. The water
'reached its level' around 1979. The resulting lake is used by divers, who
are prepared to travel from far and wide to Dorothea as it is one of the few
places where deep water is available. Unfortunately this has a down side - a
number of divers have been killed there.

The current owner of the site has been planning for some time to 'redevelop'
the site but this is likely to be at the cost of the archaeology. I believe
the most resent planning applications were for a 'Diving Centre', a golf
course on the (flattened) tips and the removal of tips for road fill. There
has also been talk of a hotel (or similar) on the site of the mill.

The Engine and several features, such as the slate 'Pyramids' (Cableway
Bases) and the mill are protected by Scheduling.

Hope this all make sense, it is written in haste, but I am putting
information together for a webpage, including photos inside the enginehouse
and the interior of one of the boilers. There are numerous websites for
divers the refer to the quarry (Hazel - would you like to do the honours).

Andrew