Title: Comment on: 'Determination of the angle of a Fisher distribution which will be exceeded with a given probability' by P. L. McFadden
Abstract: McFadden (1980) provides the basis for a simple, objective exclusion test that may prove useful to palaeomagnetists.Figs 1 and 2 illustrate the problem.Both are hypothetical, but are meant to portray situations that arise not infrequently in palaeomagnetism.Both are plots of directions of remanent magnetization from single sites (individual lava flows, sills, dykes, sedimentary layers, etc.), after magnetic cleaning.Each shows a well-defmed cluster, with one aberrant direction.Faced with situations like these most palaeomagnetists will first examine the aberrant specimen for some evidence of 'peculiarity'.(Is it weathered or otherwise altered?Does it have an unusually high intensity, suggesting that it has been affected by lightning?Could it have been collected from a,displaced (rotated) block?Has it been baked and remagnetized by nearby intrusions?Could it be from another unit?)Finding none, most palaeomagnetists will next search their souls and field notes for indications of gross error