The context and details of clasts from Figures 5(E) and 7(B). (A), (B) Plane and polarized light micrographs of the sediment, respectively, showing various rectangular clasts oriented parallel to the bedding (red arrows) within a heterogeneous mass of pseudomorphed volcanoclastic material (translucent in (A), blue in (B) indicating silica) and carbonaceous matter (black). The black box shows the location of details in (C), (D). (C), (D) In these plane and polarized light micrographs, the clast of interest exhibits a rhomboidal outline, possibly reflecting a fragment of volcanic glass rather than a feldspar fragment (the latter would be more rectangular). The clast is outlined by black carbonaceous matter. The polarized light micrograph in (D) has a speckled texture owing to the microcrystalline nature of the quartz (= chert).