File:Conglomerate & slate (Wickersham Grit, Neoproterozoic-Cambrian; roadcut between Fox and Livengood, Alaska, USA) 1.jpg

English: (photo by James Cheshire)

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Seen here are talus pieces of quartzose conglomerate and reddish slate. They were eroded from the Wickersham Grit, which is an informal name for a succession of mixed siliciclastic sedimentary rocks of ~latest Proterozoic to Early Cambrian age. The red slate is the result of low grade metamorphism of shale. The conglomerate consists of mostly angular- to subangular-shaped quartz clasts (they appear to be mostly small pebbles and granules). Conglomerate is "supposed" to be dominated by rounded and subrounded clasts. A poorly sorted siliciclastic sedimentary rock with angular clasts is supposed to be called a breccia. These samples do have a few subrounded clasts, but most are angular to subangular. If both fundamental clast shapes are present, the rock is still called a conglomerate. The British Geological Survey goes further - they reject the term "breccia" for angular-clast bearing sedimentary rocks. They assert that identification of clast shape is highly subjective - this is not true. The basic four categories "rounded", "subrounded", "subangular", and "angular" are pretty clear-cut. Regardless, a rock like that seen here can be called "conglomerate" or "breccia", depending on the classification scheme.

The term "grit" ("gritstone"; "gritrock") has no fixed definition in geology. Grit traditionally referred to sandstones having angular sand grains. It can also refer to angular clast-bearing granulestones or simply pebbly sandstones. Other definitions/usages are also known.

Stratigraphy: Wickersham Grit, upper Neoproterozoic to Lower Cambrian

Locality: Route 2 roadcut between the towns of Fox and Livengood, east-central Alaska, USA