S.J. Kluiving, A.L.L.M. Verbers, and W.J.F. Thijs. 2010. “Lithological Analysis of 45 Presumed Pingo Remnants in the Northern Netherlands (Friesland): Substrate Control and Fill Sequences”. Netherlands Journal of Geosciences 89 (July):61 - 75. https://doi.org/10.1017/S0016774600000822.