Answer sheet for the take home exam. One point was given for the correct master horizon as shown (6). Full credit was given for C or CR for the 25 to 32 inch horizon. One point was given for each of the correctly labeled B horizons that have a "t" (3). One point was given for correctly numbering the Bt horizons. Total 10 points.
The A horizon is a mineral horizon that has granular structure, is very friable and has no clay films. It is the same color as the first Bt horizon, but the structure, texture and lack of clay films differentiates it from the lower horizon. Each of the Bt horizons has blocky structure, more clay than the overlying horizon (increasing clay to the bottom), and clay films. The clay content and clay films identify the horizons as Bt horizons. The C has no clay films and therefore does not rate the Bt designation. It could be called a CR if it had any characteristics of the underlying bedrock. The lowest horizon clearly is rock and gets the R label.
SMILO SERIES
TYPICAL PEDON: Smilo cobbly sandy loam - rangeland. (Colors are for dry soil unless otherwise noted.)
A
--0 to 2 inches; dark brown (10YR 4/3) cobbly sandy loam, dark brown (10YR 3/3) moist; weak fine granular structure; soft, very friable, nonsticky and nonplastic; common fine and very fine roots; few fine vesicular pores; 10 percent pebbles, 15 percent cobbles; moderately acid (pH 6.0); clear smooth boundary. (2 to 4 inches thick)Bt1
--2 to 8 inches; dark brown (10YR 4/3) loam, dark brown (10YR 3/3) moist; weak fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common fine and very fine roots; few fine tubular pores; few thin clay films lining pores and on faces of peds; neutral (pH 7.0); clear smooth boundary. (5 to 9 inches thick)Bt2
--8 to 15 inches; dark yellowish brown (10YR 3/4) cobbly clay loam, very dark grayish brown (10YR 3/2) moist; moderate fine blocky structure; very hard, firm, sticky and plastic; few fine and common very fine roots; common fine tubular pores; moderately thick clay films lining pores and on faces of peds; 10 percent pebbles, 15 percent cobbles, 5 percent stones; neutral (pH 6.6); clear smooth boundary. (5 to 10 inches thick)Bt3
--15 to 25 inches; dark brown (7.5YR 4/4) very cobbly clay, dark brown (7.5YR 4/2) moist; moderate medium blocky structure; very hard, firm, sticky and plastic; few fine and common very fine roots; moderately thick clay films lining pores and on faces of peds; 10 percent pebbles, 20 percent cobbles, 5 percent stones; neutral (pH 6.8); clear smooth boundary. (8 to 13 inches thick)C
--25 to 32 inches; dark brown (7.5YR 4/4) gravelly clay, dark brown (7.5YR 4/2) moist; massive; very hard, firm, sticky and plastic; few very fine roots; 15 percent pebbles; neutral (pH 7.0); abrupt irregular boundary. (0 to 10 inches thick)R
--32 inches; basalt, lava flow.For those of you interested in Soil Taxonomy here are the diagnostic horizons:
Mollic epipedon: The zone from 0 to 8 inches.
Argillic horizon: The zone from 2 to 25 inches.