A borehole sunk in 1920–21 at Apedale, North Staffordshire, unexpectedly proved a tuff-dominated sequence, at least 840m thick, below a thin cover of Silesian sedimentary rocks. The tuffs were initially interpreted as Dinantian in age. However, there are similarities of form and lineament between an aeromagnetic anomaly centred upon Apedale and anomalies in the Welsh Marches associated with Neoproterozoic (Uriconian) rocks, suggesting that Neoproterozoic rocks occur at Apedale and that the tuffs in Apedale Borehole might also be of this age. Recent modelling of geophysical data shows that Apedale is underlain by two (magnetic) volcanic bodies — a deeper ridge of probable Uriconian rock, and a shallower, broadly stratiform body which includes the tuffs in the Apedale Borehole. Comparison of the tuffs at Apedale with others in the region suggests that they are of P1a (late Asbian to early Brigantian) age. Although our knowledge of the extent of the Apedale tuffs is poor, their thickness shows that they erupted from one of the largest centres of Dinantian volcanism in central England. The trace element geochemistry is very similar to that of Dinantian volcanic rocks in southwest England.

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BUSBY, J.P. and DABEK, Z.K. 1986, Resistivity and I P Modeling of the Three-Array DownHole Prospecting Technique, Geophysical Prospecting 34, 130-140.The resistivity and induced polarization responses due to a number of IP targets for a down-hole three-array have been calculated numerically. The IP targets are approximated by triangle-faceted polyhedra; number and size of the facets are limited by the numerical procedure. Despite this limitation a number of profiles have been obtained for a sphere, lens, prolate spheroid and thin dipping slab. The profiles obtained do not differentiate between the shapes of the IP targets, but depend upon the vertical extent of the target within the searchradius of the borehole. The type curves produced could be of use for preliminary interpretation and in the field for planning the next stages of a geophysical survey.The lateral and vertical search radii of the borehole are increased by the use of such an array. For the bodies used it is estimated that the search radii are extended by 2.0 dipole units.