THE DETERMINATION OF THE DIRECTION OF TRANSPORT OF FLUVIATILE ARENITES BY ORIENTATION ANALYSES OF THE DETRITAL MICA

A simple method of determining the strike and dip of the AB planes of mica flakes in etched slides of arenaceous sediments by means of a universal stage mounted on a stereomicroscope is described. The polar stereograms constructed from such measurements in fluviatile sandstones show monoclinic symmetry due to up-current imbrication which compares well with the orientation of plant fossils, current bedding structures and the general current pattern. An angular discordance exists between these features and the direction of sole marks. An example is given of how analyses of the orientation and imbrication of mica flakes can assist in the solution of sedimentation problems of coalfield geology.     

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On propagation of love-type waves on a spherical model with rigidity and density both varying exponentially with the radial distance

Summary The propagation of Love type waves on a spherical model' in the mantle of which the rigidity and density vary exponentially with the radial distance while in the core they remain constant — has been investigated. The frequency equation that has been worked out has been examined in detail for the existence of root in the particular cases when they involve Bessel Functions of smallest and largest orders.     

Franz Zorell †

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Franz Zorell

     

ELECTROMAGNETIC RESPONSE OF A BROKEN ORE-VEIN (MODEL STUDIES)*

A broken ore-vein is very common in nature. A small scale model of such a vein has been made by placing two thin metal sheets edge to edge with an air gap between them. The electromagnetic response of this model in a uniform oscillating magnetic field has been measured. The results show that (a) the response of the whole body is not the sum of responses of the constituent parts, (b) the response of the upper part is dominant by virtue of its proximity to the receiving coil and (c) the lower part has the effect of making the upper part appear nearer to the surface and poorer in conductance than it really is.     

Single-domain magnetite in the Jimberlana Norite,Western Australia

The feeder series gabbros of the Jimberlana Norite possess a large, stable NRM. Koenigsberger ratios of 20 or greater suggest that single-domain grains carry most of the NRM. Coercivity spectra extend up to 2000 Oe. Volumes of magnetite satisfying single-domain requirements occur principally as intergrowths of host magnetite between exsolution phases. Small discrete magnetite grains do occur in the Ca-rich pyroxenes but are thought to contribute only a minor fraction of the NRM.