In the USCS, gravels (given the symbol "G") and sands (given the symbol "S") are classified according to their grain size distribution. For the USCS, gravels may be given the classification symbol "GW" (well-graded gravel), "GP" (poorly graded gravel), "GM" (gravel with a large amount of silt), or "GC" (gravel with a large amount of clay). Likewise sands may be classified as being "SW", "SP", "SM" or "SC". Sands and gravels with a small but non-negligible amount of fines (5–12%) may be given a dual classification such as "SW-SC".