The St. Erth Formation: Geometry of the deposit and micropalaeontology

In 1999 a paper was presented to the Ussher Society which described, in some detail, the location of the St Erth Formation and the history of the minerals workings. At that time the authors described the results of a resistivity survey across part of the area, which, it was hoped, would locate in-situ sands and fossiliferous clays. In October 2003, using the same equipment (an ABEM Terrameter and Lund Imaging System), further lines have been documented which provide more data on the distribution of the marine sediments of Late Pliocene age. In conjunction with this additional survey work a number of shallow cores were drilled in an attempt to locate the fossiliferous clays that, since 1886, have been known to lie in this area. In most cores only wet moulding sand was recovered. In two cores thin clay interbeds were found and a limited marine fauna of foraminifera identified. Associated with these foraminifera are abundant bolboformid-like microfossils. At a location close to the site of the trench excavated by Prof. G.F. Mitchell in the 1970s a few samples of weathered clay were recovered by hand auger. These samples also contain abundant foraminifera and 'bolboformids'. Samples collected by Millett during the original quarrying operations, and which are in The Natural History Museum (London), also contain beautifully preserved foraminifera and a diverse assemblage of these unusual 'bolboformids'.