[19] For example, in the Big Horn Mountains of Wyoming.
[20] It should be noted that it is the change of temperature of the rock surface, not the change of temperature of the air above it, which is to be considered. Many data concerning temperature changes are to be found in Bartholomew’s Atlas of Meteorology.
[21] Buckley. Wisconsin Survey, Bull. IV, 1899, pp. 81–3.
[22] Livingstone has reported that the temperature of rock surfaces in Africa sometimes reaches 137° Fahr. during the day, and cools sufficiently at night to split off blocks of 200 lbs. weight.
[23] Buckley. Surv. of Wis., Bull. IV, pp. 19, 20.
[24] For an excellent discussion of erosion in dry regions see Walther’s Die Denudation in der Wüste.
[25] On the assumption that condensation takes place at an average elevation of 3000 feet, it has been estimated that the force necessary to evaporate and diffuse the moisture which falls as rain and snow would be equivalent to 300,000,000,000 horse-power constantly in operation. (Strachey, Lectures on Geography, p. 145.)
[26] McGee. Bull. Geol. Soc. Am., Vol. VIII, pp. 87–112.
[27] For a discussion of convex and concave erosion slopes see Bain, Geol. Surv. of Ia., Vol. VI, p. 449.
[28] Great rivers, like the Mississippi, cut their channels somewhat below sea-level, but probably not by an amount exceeding the depth of the stream itself (see p. 79).