22 CLIMATE AND RESOURCES OF 



cultivation was removed; thus demonstrating the greater 

 density and impermeability to water of the soil immediately 

 below the loosened arable soil, compared with the soil at a 

 greater depth, which is not to so great an extent affected by 

 the treading of cattle on the surface. The more consolidated 

 soil constitutes the pan ; its greatest density is immediately 

 below the soil broken up mechanically in cultivation, and it 

 gradually decreases in density until it becomes undistinguish- 

 able from the natural condition of the soil below it. 



To return to our wheat field. Water is again turned on, 

 the loose surface-soil is converted into a liquid mud, and is 

 carried by gravitation and deposited in the fissures made by 

 the heat on drying up, after it had on the previous occasion 

 been irrigated. This process is repeated time after time, until 

 every pore of the soil is plugged up, and the land becomes 

 almost hermetically sealed. In this state of the soil healthy 

 action is impossible. 



The crop is reaped in March or April, when the surface-soil 

 presents a smooth glazed appearance, in the very best possible 

 physical condition for retaining and reflecting heat ; and in 

 the very worst possible physical condition for absorbing and 

 radiating heat. In fact, we have brought the soil into a 

 condition as much resembling stone as possible, and in this 

 state it remains during the hottest months of the year, 

 increasing the intensity of the heat, until the rains commence. 



The consequence of this is, that when the soil has become 

 heated by the sun during the day it cannot part with its heat 

 at night by radiation, as a loosened soil would ; the following 

 day the rays of the sun fall on a still warm surface, instead of 

 a surface chilled by radiation, and less solar heat is required 

 to raise its temperature, and eventually the temperature of 

 the atmosphere, to a degree obnoxious both to animal and 

 vegetable life. 



