|
Introduction:
Stone-slate geology
Stratigraphy
Rocks
and climate
Map
Cretaceous
- Wealden
Jurassic
Permian and
Triassic
Carboniferous
Devonian - Old
Red Sandstone
Silurian
- Pridoli: The Tilestones
Ordovician
|
| The Devonian
or Old Red Sandstones are found from Cornwall to Shetland and although
they were only used for roofing in a few locations some of these were very
large industries producing a range of products, especially flagstones for
18th and 19th century towns and cities World-wide. The most important quarries
were in Caithness and at Carmyllie in Tayside but they have also been significant
sources of stone-slates in the Welsh Marches and South Wales. |
GEOLOGY
The geology of the Silurian - Devonian
boundary is difficult and has taken a long time to unravel. This has lead
to a lot of debate about the exact position of the 'boundary' formation,
the Downtonian. It was previously placed at the bottom of the Devonian
but is now at the top of the Silurian - in the Pridoli, so care is needed
when using older texts and maps. |
|
Devonian
geology is differentiated into five main units but one of these is only
present in England and one only in England and Wales
|
| Carboniferous |
|
|
| |
Upper Devonian
and Upper Old Red Sandstone |
|
| |
Limestone |
England only |
| Devonian |
Middle Devonian.
Middle Old Red Sandstone |
|
| |
Lower Devonian |
England and Wales
only |
| |
Lower Old Red
Sandstone |
|
| Silurian |
|
|
|
WALES AND
THE MARCHES
In Herefordshire and South Wales
the sandstones from the St Maughans formation in the Dittonian period of
the Lower Old Red Sandstone have been quarried at many sites producing
a variety of stone-slates ranging from a grey-green to a distinctive red.
The stone was worked in small surface quarries close to the point of use
and roofs are found with single colours or mixtures. These reflect the
local geology which varies on a large and small scale so when conserving
these roofs it is difficult, and possibly un-necessary, to try to be too
precise in defining the colour of stone to be used. There were quarries
all over the region. Some of the more well known are around Llanveynoe,
Abbey Dore and at Garnons and Dinmore Hills. |
| Roofs in the region are always simple,
gable to gable, with even valleys being comparatively rare. There are many
buildings which need roof renovations and fortunately quarries have recently
been established which can supply both colours. However they are only operating
on a small scale and it will be important for owners and specifiers not
to overwhelm them. It is in situations like this, and there are many examples
through the country, where it would be useful if English Heritage, local
conservation authorities, church architects, estate owners etc. could develop
a plan for roof conservation in the region to ensure supply and demand
are in phase. |
 |
Howe
recorded stone slates from the Old Red Sandstone marls of Stockholm, Pembrokeshire
(where) thin sandy layers are obtained, and formally were made into roof
tiles. These were very small and irregular in shape, but nothing could
be more lively in effect than their mottled buff, red and grey, with occasional
white micaceous sheen. (It is possible that these are from the Downtonian
and would now be in the Silurian.)
Top |
SCOTLAND
The Lower
and Middle Old Red Sandstones have both been worked for stone slates in
Scotland. The former in Angus, now Tayside, and the latter in Caithness
and the Northern Isles. |
ANGUS
East of Arbroath
in Tayside (Angus) a large industry developed in the Lower Sandstone. As
early as 1678 Robert Edward, Minister of Murroes, wrote that there were
many quarries in Angus, producing high quality stone, some of which was
shipped to Fife and the Lothians, Holland and North America. (see Mackie).
The industry developed with production increasing substantially in the
early 19th century in part due to mechanisation, with the introduction
of cutting, planning and edging machines. A machine was even developed
to make stone railway sleepers but was abandoned when wooden sleepers became
the standard. Problems were encountered with ground water as the quarries
deepened and the region became famous for the many windmills used to pump
water from the lower levels. |
| 'The eye is first caught, in approaching
them, as we surmount a long flat ridge, which shuts them out from the view
of the distant sea, by what seems a line of miniature windmills, the sails
flaring with red lead, and revolving at the slightest breeze at more than
double the rate of the sails of ordinary mills.' Hugh
Miller 1841 |
|
| In 1854 a
railway was constructed to carry stone from the Carmyllie quarries to Arbroath.
By 1859 it was carrying 150 tons a day. Nowadays the quarries are only
operated occasionally. |
| The quarries
produced masonry, including carved and turned products, roofing, flagstones
and became famous for the latter shipping large quantities all over the
world. |
| '....
in various districts of the Seedley Hills there are numerous strata of
sandstone flags, which may be raised of various thickness and dimensions.
The thinnest of them are from about half an inch, to an inch in thickness.
They are formed into plates of about fourteen or sixteen inches broad and
eighteen or twenty inches long and are used for roofing houses. These plates
are coated with scales of mica, or talc, of a greyish-blue colour, and
this occasions the easy separation of the plates from each other; but after
long exposure to the air, they assume a grey or brownish colour.'Rev
James Headrick 1813 |
|
| The size quoted
for the roofing slates was typical although they would have been sold as
randoms. In 1837 a mix of 15 to 20 inches long by 9 to 12 inches wide cost
£4.10s per thousand. Selling random sizes by the thousand must have
been the cause of disputes and may explain why Reverend Headrick reported
that 'they seldom make a roof that is ..... watertight.' If the roofer
received more small sizes than he had reckoned on he would be tempted to
reduce the head lap to make them cover the slope with the risk of leaks.
Historically the local name for stones slates is sclaits
as against sclalyie or skalzie for metamorphics. Stone slates were used
throughout the quarrying region but were also shipped to other towns along
the Scottish coast. |
CAITHNESS,
ORKNEY AND SHETLAND
The Middle
Old Red Sandstone has been used as a local building material in Orkney,
Shetland and the north-east of Caithness but it was in the latter that
it became a substantial industry. Locally, it was used for many purpose
- '... the houses have been built, the roofs slated, the roads paved, the
fields fenced and the drains lined so varied are the uses to which the
rocks are adapted'. |
| In its products
and development the Caithness industry mirrors that of Angus although it
was later in starting to export - the first shipments were dispatched in
about 1824. However, it grew to become very substantial. By 1845, Castlehill
Quarry alone, which had opened in 1824, was employing 100 labourers and
exporting 3000 to 4000 tons of flagstones. The peak years for the region
were 1901/2 when nearly 35,000 tons of all products were manufactured but
in the same period employment fell from 500 to 414. |
| Two rocks were exploited for roofing:
a 'very hard, thin, dark micaceous flag' and a 'pale green, thin flag or
"slate" much in demand lately for artistic work on churches and public
buildings, and is exported from Thurso to England.' (British Geological
Survey Memoir: Caithness. Crompton). The green
stone slates were produced at White Moss quarry. |
| Eventually
the industry declined as metamorphic slates became more readily available
and concrete products took the market for flagstones. More recently there
has been a revival and stone roofing and all the other products are available
again. |
British
Geological Survey Memoir: Geology of Caithness C B Crampton and R G Carruthers.
1914 Caithness Flagstones.
|
|
|
