It averages between 12 and 18 percent clay and between 45 and 80 percent sand. Reaction ranges from moderately acid to very strongly acid. Some pedons have a BC horizon. The C horizon has hue of 10YR or 7.5YR, value of 4 through 6, and chroma of 2 through 8, and commonly contains iron and manganese stains or accumulations. It is stratified sand to loam and some pedons contain a component of gravel or thin strata of gravel.
Reaction ranges from moderately acid to mildly alkaline and some pedons contain carbonates.
Roby is the only series in this family. Soils in similar families are the Ayrshire , Badaxe , Bronson , Hayfield , Homer , Ridgeville , Udolpho , and Whitaker series. Ayrshire and Whitaker soils have chroma of 2 in the E horizon and contain more clay and less sand in the control section. Badaxe soils are underlain by calcareous loamy glacial till and do not have strata or sand textures in the lower part of the solum or in the substratum. Bronson soils contain coarser sand and contain some fine gravel throughout the solum.