Average sand content ranges from 35 to 50 percent. These are the Clyde , Faxon , Selma , Selmass , Tripoli , and Webster series. Clyde soils are in cooler and drier climates and do not have rock fragments dominantly of sandstone, siltstone, and shale. Faxon soils have a lithic contact within a depth of 40 inches. Selma and Selmass soils average more than 50 percent sand in the lower part of the series control section.
Tripoli soils lack rock fragments in the upper part of the series control section.
Webster soils are in cooler and drier climates and typically have thinner sola. Competing series may change as they are updated to the 8th Edition of Keys to Soil Taxonomy. The Free , Kossuth , Reddick , Springerton , and Wolcott series have not been updated to the 8th Edition of Keys to Soil Taxonomy, but were competing series to Marengo under previous taxonomic classification. Free soils have more than 15 percent rock fragments in the lower part of the solum. Kossuth soils have more than 35 percent clay in the upper part of the series control section.