Every prehistorian has heard of the famous volcanic rock of the Eifel from which querns were made in prehistoric and later times. The source from which the querns came has several names, and we read of Andernach, Niedermendig and Mayen lava. Actually, Andernach is merely the Rhineland town nearest to the quarries; there is no lava there. Niedermendig has lava quarries, but they did not begin to be worked until the Middle Ages, and then the output was only about one third of that of Mayen. Since however the output of Mayen passed through Niedermendig on its way to the Rhine, the latter name got attached, and we in Britain usually write of ‘Niedermendig lava’. But all prehistoric and Roman querns came, not from there but from the Mayen quarries, which are still being worked. During a visit to Germany in July 1953, I was conducted round them by Dr J. Röder of Koblenz. The following account, though made possible by that visit, is not an original composition but is derived from an authoritative article by Dr Röder and others, which has kindly been abstracted for me in English by Mr J. D. van der Waals of Amsterdam. I wish also to thank Dr Röder for the loan of illustrations, especially the blocks for FIGS, 1 and 3.