There is much more information about rock art on the England’s Rock Art website and on the Beckensall Archive.
You can download a brochure ‘The Prehistoric Rock Art of England: Recording, managing and enjoying our carved heritage’ (pdf). Produced by the Northumberland and Durham Rock Art Pilot (NADRAP) Project.
A Rock Art Bibliography (pdf) is also available to download from England's Rock Art website. This detailed listing contains over a thousand publications on rock art. It relates primarily to rock art in the counties of Durham and Northumberland but also includes many publications on rock art in other parts of Britain and Ireland, as well as on the recording, management, and conservation of carved panels, plus a number of theoretical studies.The bibliography was compiled by NADRAP volunteer Keith Elliott, with additional contributions from Kate Sharpe and Aron Mazel.