| Computer Code: |
PDS |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Famennian Age (DA)
— Famennian Age (DA) |
| Lithological Description: |
Purple, red-brown and greenish-grey sandstones, commonly current bedded and generally fine to medium grained. Subordinate red and grey cleaved mudstones predominate at the base and top of the formation: fish fragments have been found towards the base of the formation where it is exposed on the coast; plant fragments have been found inland. Base of the formation is marked by a sporadic but persistent band of tuff (Bittadon Felsite), up to 8 m thick, the type locality of which is alongside the driveway to Hewish Barton [SS 5502 4086] which is massive, slighty foliated, fine- to-coarse grained with iron oxide spots and broken feldspar laths. |
| Definition of Lower Boundary: |
Overlie Morte Slates; the base of the formation is marked by a persistant keratophyric tuff band up to 8 m thick which is massive and strong where fresh, and forms a distinct topographic feature. The lower boundary is distinguished by a change from the grey cleaved mudstones of the Morte Slates to the massive, slightly foliated fine- to coarse-grained tuff. |
| Definition of Upper Boundary: |
At Napps Cliff [SS 4460 4072] the contact is stratigraphic and gradational over approximately 9 m of strata; progressively higher sandstones become thinner and finer-grained and give way to predominant siltstones, silty slates and slates in the Upcott Beds. |
| Thickness: |
Approx. 1200 m. |
| Geographical Limits: |
South-west England: from Morte Bay [SS 4545 4175] on the north Devon coast in a west-south-west trending outcrop of variable width as far east as Langley Marsh [ST 0718 2848]. |
| Parent Unit: |
Not Applicable (-)
|
| Previous Name(s): |
Pickwell Down Sandstones [Obsolete Code: Use PDS]
(PWS)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Area |
Bittadon Felsite - quarry alongside the driveway to Hewish Barton. Salter, 1863. |
| Type Area |
Pickwell Down. Edmonds et al., 1985. |
| Reference(s): |
| Edmonds, E A, Williams, B J, and Taylor, R T. 1979. Geology of Bideford and Lundy Island. Memoir of the Geological Survey of Great Britain, Sheets 292 with 275, 276, 291, and part of 308 (England and Wales). |
| Etheridge, R. 1867. On the physical structure of west Somerset and north Devon and on the palaeontological value of the Devonian fossils. Quarterly Journal of the Geological Society of London, Vol. 23, 568-698. |
| Salter, J W. 1863. On the Upper Old Red Sandstone and Upper Devonian Rocks. Quarterly Journal of the Geological Society, Vol. 19, p 479. |
| Bonney, T G. 1878. Note on the felsite of Bittadon, north Devon. Geol. Mag., Vol. 15, 207-209. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
