An area of the crest of the Carlsberg Ridge, the mid-ocean ridge in the northwestern Indian Ocean, has been surveyed in detail; the area measures 50 by 38 nautical miles. Contour maps and profiles show the results obtained with a precision echo-sounder and a proton magnetometer. Within the surveyed area, a dextral tear fault displaces the median magnetic anomaly and the median valley through about ten miles. Fresh basalt lavas have been dredged from the area together with metamorphosed basaltic rocks. Brecciation and hydrothermal alteration of the crustal rocks in a comparatively wide fault zone may explain why the pattern of magnetic anomalies seems to have been expunged along the fault.