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SOP No. 210 Page 5 of 7 2.5 Geologic Modifiers Sedimentological descriptions aid in the geologic classification of a soil material. Only insert geologic modifiers when present. Stratification: Note the presence and thickness of alternating layers of non-cohesive materials of different grain sizes and/or color with layers at least 6 mm thick. Lamination or Varves: Note the presence and thickness of alternating very thin layers of fine materials or color, such as silt and clay, with layers less than 6 mm thick. Sorting: A geological term used to describe how close in size the grains in a sample are to each other. For example, a well sorted sample contains grains of similar size; a poorly sorted sample contains grains of many sizes. Angularity or Rounding: Geological terms that are used to describe the general appearance of visible grains in the soil sample. Useful in determining the origin and depositional environment of a material. Water transported materials may be rounded. Glacial tills will be more angular. The following terms describe differing degrees of angularity: • angular — particles have sharp edges and relatively plane sides with unpolished surfaces; • subangular—particles are similar to angular description but have rounded edges; • subrounded —particles have nearly plane sides but have well-rounded corners and edges; and • rounded—particles have smoothly curved sides and no edges. Shape: A term used to describe the shape of gravel, cobbles, and boulders. Terms are as follows where the particle shape shall be described where the length,width,and thickness refer to the greatest, intermediate, and least dimensions of a particle: • flat—particles with width/thickness > 3;