SPEARMAN, R M; WILTHEW, Paul; O'NEILL, Marion. The Helmsdale bowls, a re-assessment. Proceedings of the Society of Antiquaries of Scotland, [S. l.], v. 120, p. 63–77, 1991. DOI: 10.9750/PSAS.120.63.77. Disponível em: https://journals.socantscot.org/index.php/psas/article/view/9379. Acesso em: 25 apr. 2024.