Arkæomagnetisme og jernalderslagge

Archaeo-Magnetism and Iron-Age Slags In the first three sections a short review is given of magnetic concepts and their use in archaeomagnetic dating and finding, while in the last section an example on their application is given: Slag pits from prehistoric iron-smelting have earlier (Voss, 1962) been excavated at Drengsted in Southwestern Jutland (fig. 6) and some of them C-14-dated on carbonized straw or charcoal to the age of 210 ± 100 A.D. or to the interval between 320 and 410 A.D. while potsherds and a settlement at the same place indicated an age of the 5th century A.D. Hence it is for the moment doubtful whether the settlement and the iron-smelting are of the same age or not. Planning new excavations in the same area it was then decided, as the slag pits are strongly magnetic to make arealmagnetic measurements as well as paleomagnetic determinations; none of these methods have formerly been applied in Danish archaeological work, wherefore collaboration between Forhistorisk Arkæologisk Institut and Geologisk Institut at the University of Aarhus was started.The instrument available at the moment was an Askania-Gfz-vertical-intensity-magnetometer, with which an area of 40 X 80 m2 as shown in red in fig. 7 was measured, and to compare the reliability of the method part of the same area was remeasured with a denser net of measuring-points as shown in fig. 8; the mean-error at a point is ± 4 gamma, while most of the positive anomalies lie between 20 and 100 gramma. Afterwards the northern half of the area was excavated and revealed 47 slag pits (fig. 7) 19 of which were undisturbed (full black dots), while the rest were broken up but still lying in their original places, the slags being between 0.6 and 0.9 m in diameter and with weights up to 450 kg. To determine in detail the magnetic anomaly of typical, unbroken slag pits, two small, isolated anomalies were selected in the undisturbed southern part of the area and remeasured detailed, the anomalies of which turn