EROSION IN ARIZONA BOLSON REGION I5I 
experiments in dry farming show how a moisture table, elevated far 
above the water level, can be developed and protected by cultivation.* 
The crust deposits of the semiarid regions are believed to be developed 
by a similar moisture table. The rainwater penetrates with difh- 
culty the dry soil, and while a portion may gain the larger openings 
and sink to the underground water level, a larger portion is caught 
in the capillary pores and drawn upward by the drying-out above, 
and laden with mineral salts deposits its load as the ‘‘caliche’’ crusts,? 
through evaporation at or near the surface. ‘These crusts are built into 
the deposits, and are slowly recrystallized, forming the calcareous, 
gypsiferous, and even siliceous cement of the cement-gravels. The well 
sections examined in the vicinity of Tucson show that the amount 
of the cemented gravels may rise to 80 per cent. of the whole. 
Possibly the “mortar beds” of the high plains of Kansas, for which 
Johnson could find no adequate explanation’ were surface crusts 
formed under local conditions of aridity, by means of an actively 
evaporating moisture table, and covered by subsequent deposits. 
CLIMATE 
I believe that in the future, when the recognition of climatic effects 
in sedimentation becomes general, the value of the recent articles 
by Barrell and Huntington‘ will be highly rated. Climate itself, 
however, needs still further analysis before its effects can be read 
satisfactorily in the strata. The critical factors from the erosional 
and depositional standpoint have not yet been determined, especially 
those that are in a measure the independent variables, nor has the 
t See Bulletins 103 and 130, Bureau of Plant Industry; also Livingston, “‘The 
Soils of the Desert Laboratory Domain,” Publication 113, Carnegie Institution of 
Washington; Bulletin Agricultural College of Utah, No. 91; Alway, “Studies of Soil 
Moisture in the Great Plains Regions,” Jour. Agricultural Science, Vol. I], pp. 333-42. 
2 For description and discussion of the caliche see Blake, Trans. Am. Inst. of 
Mining Engs., Vol. XXXI, pp. 220-26; Tolman, Joc. cit.; Lee, Water Supply Papers, 
INOMT3O" Wio) GaSe ips 1 Ll 
3 Op. cit., pp. 643-57. : 
4 Barrell, “The Relation between Climate and Deposition,” cited above; ‘‘ Rela- 
tive Importance of Continental and Marine Sedimentation,” Jour. of Geol., Vol. XIV, 
1900, pp. 316-56, 430-59, 524-68; Huntington, ‘“‘Some Characteristics of the Glacial 
Period in Non-Glacial Regions,” Bull. Geol. Soc. Am., Vol. XVIII, pp. 351-85. 
