SOIL MOISTURE AND TO EVAPORATION. 23 



During the summer rainy season of 1904 the surface soils of 

 Tumamoc Hill were often wet and almost continually moist. As has 

 been noted, it is probable that during the heavy showers considerable 

 quantities of water penetrate to the deeper soil masses along rock 

 surfaces and a relatively large amount is often held for several days in 



TABLE II. Mean Monthly Precipitations at Tucson, Arizona. 



TABLE III. Precipitation Record from May g to December 31, 1904.. 



hollows of the soil, so that time is allowed for direct penetration 

 downward. Nevertheless, it must be remembered that, owing to the 

 relatively low permeability of these soils, a large proportion of the 

 water which falls in the heavy rains fails to soak into the puddled sur- 

 face and finds its way to the mesa below, where it rapidly drained 

 away to the Santa Cruz. 



But, from the facts presented in the discussion of the water con- 

 tent of this soil it is clear that what water does attain to the depth of 

 half a meter or more is well protected from soil evaporation and will 



