R.T. Van Balen, J.M. Verweij, J.D. van Wees, H. Simmelink, F. Van Bergen and H. Pagnier (2002) “Deep subsurface temperatures in the Roer Valley Graben and the Peelblock, the Netherlands - new results”, Netherlands Journal of Geosciences, 81, pp. 19-26. doi: 10.1017/S0016774600020539.