9 



in the narrow.* Since all of these stations are located near the floor 

 and represent siiccessional stages in ravine development, the data 

 suggest a movement from moderate moisture conditions in the em- 

 bryonic ravine to greater moisture in the narrow portion, with a 

 reversion to slightly drier conditions as the ravine changes from the 

 \'-shaped to the U-shaped type. 



2. The graphs in Figure 17 (PI. X) show that the rate of evapo- 

 ration was only about two-thirds as great at the foot of the northwest- 

 facing slope as near the top of the same slope, and that there was 

 little difference in the rate of evaporation for the greater part of the 

 season between the foot and the middle of this slope. The average 

 amounts of evaporation per day at the foot, middle, and near the top 

 of this slope were 4.75 c.c, 4.28 c.c, and 6.67 c.c. respectively. 

 The graphs in Figure 22 (PI. XIII) show similar results; 

 the amount of evaporation per day was 2.33 c.c. or 63.4%, 

 greater near the top than at the foot of the north-facing slope. 

 The rate of evaporation at the middle of this slope was, for 

 about the first two-thirds of the season, nearly the same as 

 near the top. The graphs in Figure 19 (PI. XI) show simi- 

 lar results for the opposing slope, the average amount of evapo- 

 ration per day being 4.75 c.c, 5.51 c.c, and 7.6 c.c. respectively for the 

 bottom, middle, and top of the southeast-facing slope — 2.85 c.c, or 

 60%, greater near its top than at its foot. A similar series of stations 

 in a less mesophytic portion of the ravine exhibit a similar set of con- 

 ditions to those found in the more mesophytic portion. Here the 

 rates of evaporation at the bottom, middle, and top of the north-facing 

 slope (PI. XIII, Fig. 22) were respectively 3.67 c.c, 6.36 c.c, and 6.0 

 c.c, while for the south-facing slope (PI. XIV, Fig. 24) they were 3.67 

 c.c, 5.74 c.c, and 7.93 c.c. ; that is, the average amount of evaporation 

 per day was 4.26 c.c, or 11.6% greater near the top of the south- 

 facing slope than at its foot. The graph for the daily rate of evapo- 

 ration for weekly intervals at the middle of the southeast-facing slope 

 (PI. XI, Fig. 19) is diagrammatically between the graphs for the evap- 

 oration at the foot of the northwest- and near the top of the south- 

 east-facing slopes, and likewise the graph for the rate of evaporation 

 of the middle of the south-facing slope (PI. XIV, Fig. 24) is between 

 the graphs for the foot of the north- and near the top of the south- 

 facing slopes. As already pointed out. the rates of evaporation for 

 the middle of the northwest- and north-facing slopes (PI. XVII, Fig. 

 17, and PI. XIII, Fig. 22) were not intermediary between those at 

 the foot and near the top of these slopes; the coincidences in the 



*In the computation of the percentage rates the smaller of the two numbers is 

 always used as the base. 



