- GeoRef, Copyright 2008, American Geological Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
Color variations (orange zones within buff-colored till) in drift in east-central North Dakota are believed to represent two tills of separate origin. Mean size, standard deviation, and number and type of pebbles show greater difference between the two tills than do skewness, kurtosis, and partial chemical analyses. Probably blocks of older till were moved by the last glacier crossing the area and were redeposited in a matrix of younger till.