Floor Depth Research Articles

The geological results of measurements of gravity in East Carmarthenshire

Observations of gravity over the Palaeozoic rocks of East Carmarthenshire show this to be an area of positive Bouguer anomalies, and throughout the district the isogams are aligned in a «Caledonoid» direction. The regional gradient over the anthracite coalfield can largely be explained in terms of known structure, while the anomaly values in the Towy valley above Llandeilo seem to have been affected by facies variations and contemporaneous volcanic activity. Fairly large anomalies are recorded near Carmarthen, and these may be associated with similar anomalies known near Aberystwyth (Cook & Thirlaway, 1950); they are interpreted as an expression of the Welsh geosyncline. The gravity low discovered in St. George's Channel byBrowne & Cooper (1950) is re-interpreted in terms of the depth of the pre-Palaeozoic floor. There is no marked evidence to indicate the presence of a concealed «granitic» intrusion beneath the coalfield, nor to substantiate the view that there was once a great thickness of Permian or later cover.

Seismic investigations on the Palaeozoic floor of east England

The depth of the Palaeozoic floor under part of east England has been investigated by the refraction seismic method. Records have been taken every 200 ft. along lines 4000-8000 ft. long; such detailed shooting enables various sources of uncertainty in the results to be investigated. The interpretation of the seismic results required a more thorough knowledge of the contours of the Jurassic and Cretaceous than was available; the data from bore-holes and outcrops have therefore been collected and are presented in the form of contoured maps showing the depths of various horizons and the thicknesses of rock between them. A map of the form of the Palaeozoic floor and a discussion of its constitution are also given. The latter is based on a re-examination of the bore-hole cores and on the seismic velocities.