If you can get access to , see url below , then tha tmay help ,otherwise it might mean getting hold of Portugese books by Costas Goberna e.g. Arte Rupestre Prehistorico de Galicia in De Petroglyphis Gallaeciae , sounds like it's close . Ramon Fabregas Valcarce did a Phd at Reading a few years ago on the subject ,if you could get hold of him tha twould be good , sorry no contact info . Hopefully something will be forthcoming before September . http://links.jstor.org/sici?sici=0043-8243(199402)25%3A3%3C374%3ARARALA%3E2.0.CO%3B2-9