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Stone roofing in England update
Stone roofing in England was published in English Heritage Research Transactions Volume 9: Stone Roofing in 2003. Since then more information and some errors have come to light
  • Error. P34 Table 1. 
The entry for Surrey, Sussex, Kent should include Charlwood stone (Small Paludina limestone) not Chatwall stone.
  • New information. P74 In the Ordovician geology of Shropshire. 
At Cheney Longville an old quarry has been re-discovered at SO410852 in Longville Wood/Plantation. This may be La Touche's roofing source (1923 Field Meeting - Plowden, in Transactions of the Caradoc and Severn Valley Field Club, 7: 2, 61-3.) It has steeply dipping beds at 68 degrees with fissile rock visible. 'The quarry is in the unit known originally as the Chatwall Flags close to the boundary with the overlying Chatwall Sandstone. Nowadays they are both part of the Chatwall Sandstone Formation (Ordovician)' Graham Lott. 
  • New information. P81 Welsh Marches and Bristol - Permian
The source of roofing known informally as Grinshill Flagstone (Thompson 1993, 1995) is undefined but is believed to be equivalent to the Tarporley Siltstone Formation (Link to description on BGS website). The TSF was also formerly known as the Waterstones (BGS British Regional Geology, volume 10, Central England 3rd edition p68 et seq). The stratigraphy for the southern part of the Cheshire Basin is (old terms in brackets):

Mercia Mudstone Group:

Bollin Mudstone Fm. (ie, Keuper Marl)
Tarporley Siltstone Fm. (thought to be the Grinshill Flagstone) (Waterstones) Sherwood Sandstone Group:
Helsby Sandstone Formation (this is the Grinshill Sandstone) (Keuper Sdst)
Wilmslow Sandstone Fm. (Upper Mottled Sdst)
Chester Pebble Beds Fm. Bunter Pebble Beds)
Kinnerton Sandstone Fm. (Lower Mottled Sdst)
( Ed Hough BGS personal comment)
The 1788 painting of the old Grinshill Church accessible through the Secret Shropshire website appears to show a stone roof with a hint that the stone slates might have been bedded in mortar. This church was replaced 1839 - 40 with one in red sandstone designed by J Carlin Jun.
The thinly fissile beds in the TSF can be seen at the top of the active Grinshill Quarry.

There are no roofs known to survive today but it is possible that D C Davies FGS saw some in the early C20. Refering to the use of sandstone for roofing he commented that 'The thin calcareous flags that lie between the Bunter and Keuper sandstones in Shropshire, at Grinshill, were formerly used for the same purpose.' (Daviies D C, 1912, A treatise on slate & slate quarrying,  Crosby Lockwood, London, p77 5th ed. 

Fissile beds in Grinshill Quarry
  • Error. P82 Igneous
The attribution of the Corndon Hill stone slate as igneous is wrong. It is in fact a very fine, laminated siliceous sandstone (Graham Lott BGS personal comment). In Vernacular Buildings of Shropshire (Moran M, 2003 Logaston Press, Almeley, Herefordshire, p42 ) it is described thus: The hill itself is a large dolorite intrusion ... however on the south western slope of the hill the altered Hope Shales on the margin of the dolorite produce finely laminated material which was extensively quarried for roofing and flooring.