The Upper Cambrian shales are dark grey and black shales. The DECC (2012) 3.5 MB pdf report states that the Upper Cambrian shales have a "high organic content ... although they are probably overmature for conventional hydrocarbons".
See also the Aber Mawr Shale Formation and the Stockingford Shale Group in the BGS lexicon of named rock units.
The Upper Cambrian shales are locally present within the National Geological Model in north and west Wales and in the Midlands (Midlands microcraton).
The maximum height of the top of the Upper Cambrian shales is about 300 m above OD at outcrop in west Wales and the greatest depth is over 2000 m below OD, also in west Wales.
Please contact BGS Enquiries for more information.