Abstract

The mineralogy of the Millstone Grit sandstones is described. It is shown that the heavy mineral assemblage is quite different from those of the Upper Limestone Group and Coal Measures. Lateral variations in the accessory minerals are considered to be due to derivation from several sources rather than to sorting or to differential intrastratal solution. Vertical variations are attributed to changes in the relative importance of the different source areas. An examination of both light and heavy minerals suggests that the major source areas were composed largely of low-grade metamorphic rocks intruded by acid igneous masses and that several of the minor assemblages may have been derived by local erosion of the Upper Limestone Group.