This petrographic group includes dark reddish-brown to dark brown, non-calcareous, silty clays. The matrix is non-active, nearly opaque (isotropic). The silt component consists mainly of (angular) quartz (8–15% of the slide area), accompanied by a considerable quantity of heavy minerals (hornblende, pyroxene and especially biotite) and feldspars (plagioclase, microcline) that also appear in fine to medium sand size (heavy minerals: up to 160 µm; feldspars: up to 260 µm). The predominant non-plastic component is rounded to sub-rounded, fine to coarse quartz sand, forming 7–10% of the slide area. Grains have an average size of 250–320
µm. Occasional coarse grains (up to 900 µm) appear in virtually all samples. In several cases the quartz is strained (undulose extinction, subgrain re-crystallization). Rare inclusions are calcareous sand (mainly rounded, micritic limestone), which mostly forms less than 1% of the slide area, and the exceptional angular chert