R.H. Verschure, C. Maijer, and P.A.M. Andriessen. “Isotopic Age Determinations in South Norway: I. The Skar Volcanic Breccia, Greipstad, Vestagder”. Netherlands Journal of Geosciences, Jan. 1989, pp. 253-6, https://njgjournal.nl/index.php/njg/article/view/12901.