AbstractIn seismic underground surveys carried out by Seismos GmbH in siderite mines of Siegerland (Germany) anomalies in velocities have been found which could be explained only by the assumption of slates being aeolotropic. In this paper some of the peculiarities connected with the propagation of elastic waves in aeolotropic media–especially those consisting of thin beds of isotropic material–are discussed. Schlieren‐pictures of wave‐fronts are presented, which show the validity of the