Cumbrian slate

Kirkby-in-Furness Quarry (SD250837)

Elterwater Quarry (NY324048)

 

 Slates from Kirkby Moor in the south-west of Cumbria have been used as roofing material for over 400 years. At first production was small-scale carried out by individual tenant farmers.  However by the mid 18th century, the rising population, and rapid growth of cities during the  Industrial Revolution  increased the demand for roofing stone  and hence required larger scale and more efficient production methods. As a result independent slate operators were phased out and replaced by a single authority able to pool resources and improve efficiency. The present company Burlington Slate Co. was  established in 1843 by Lord Cavendish, second Earl of Burlington and later 7th Duke of Devonshire to extract slate from the  Kirkby-in-Furness Quarry  (SD 250837).  The arrival of the railway in Kirkby shortly after the establishment of the company greatly facilitated the distribution. of the slates. Production continued to increase reaching a peak of 15,930 tonnes in 1863.  However, in common with British slate producing areas, annual production declined from just under 10,000 tonnes at the beginning of the 20th century to less than 2000 tonnes in the 1970s. As with the Welsh industry, production has now recovered and the quarry is producing annually almost 4000 tonnes of Burlington blue slate. 

 Geological setting:   Slates are extracted from the Kirkby Moor Flags Formation. This is a thick, sorted homogeneous siltstone of Silurian age, dark blue-grey in colour with occasional beds of finer-grained material cutting across the surface. Slightly calcareous beds are common

Burlington Slate Co. also produces a green slate, trading as Westmorland,  from Elterwater (NY324048) one of several quarries in the Lake District located in the Borrowdale Volcanics.  Many of these quarries operated as independent companies in the 19th century before being taken over by larger concerns.  At one time the Lakeland Green Slate Company Ltd, operating four quarries, was the largest slate producer in the Lake District but was taken over by Burlington in 1975.  The Elterwater slate quarry and Broughton Moor, were bought initially by the Old Delabole Slate Co, and subsequently in 1976 bought by Burlington. However slate extracted from the Broughton Moor quarry is not used as a roofing material  but for other architectural uses.  

Geological setting: Westmorland slate is formed from fine-grained volcanic ash or tuff. This is part of the Borrowdale Volcanic Group, comprised of subaerial lavas, tuffs and agglomerates, which erupted in the Ordovician period between 400 and 450 million years ago. These volcanic rocks form most of the high mountains in the Lake District. Two seams of fine-grained tuffs were worked for roofing material. The lower seam, at the base of the Borrowdale Group near Honister Pass, produced grey-green slabs and the upper seam, to the SE near Ambleside, produces green slabs(Cameron 1996). The material has a high chlorite content which gives them their characteristic green and grey colours. Bedding features such as ripple marks, cross lamination and graded bedding can be seen on the  surface, making them a popular stone both for roofing and other architectural purposes.

Today, the Elterwater quarry, located in the upper seam, is the main quarry producing Westmorland green roofing slates. It employs a workforce of 7 and extracts annually over 400 tonnes of roofing slate and a similar amount for other architectural purposes. All the slate is processed centrally at the Kirkby-in-Furness Quarry.

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