No abstract

In studies of the paleosecular variation the situation often arises that, although a number of spot readings of the palcogeomagnetic field have been deduced from the fossil magnetization of a rock formation, their stratigraphic sequence is unknown. Hence, in this paper, methods are discussed of deducing the amount of dispersion produced by the palcosecular variation in the magnetization of a rock formation agains• the background of noise due to experimental errors, partial remagnefization, subsequent tectonic movement, etc. The secular variation recorded at observatories and field stations during the pas• few centuries does not cover the full range of dispersion of the geomagnetic field in time, and models are considered by means of which this may be estimated. Angular dispersion factors are defined and have been calculated for three models and found to be of the same magnitude as those calculated from various rock formations. Other calculations for these models predict that the secular variation dispersion depends on latitude, and data from a number of igneous rock formations appear to confirm this prediction. It is not possible, however, to calculate the dispersion due to the palcosecular variation from the large body of palcomagnetic data tabulated by various authors, since these data have been computed in different ways.

No abstract

No abstract

The Great Whin Sill, which was intruded in Upper Carboniferous to Lower Permian times, has been sampled at 36 sites in Northumberland and Durham. It was found to be magnetically stable, the site mean direction of magnetization being 187~.8-4".9 and the mean pole position lying in latitude 37O-3 N longitude 168O.9 E. The distribution of the mean directions of magnetization at these sites is not circular but oval, with the variation in the direction of the palaeomagnetic longitude about twice that in the direction of palaeomagnetic latitudes. However the poles calculated from the site mean directions of magnetization have a circular distribution, and this observation leads to proposal of a method of calculating the errors associated with the palaeomagnetic pole positions.