【正文】 uge aquifer (a rock layer containing large quantities of groundwater).160. The Ogallala aquifer is a sandstone formation that underlies some 583,000 square kilometers of land extending from northwestern Texas to southern South Dakota.161. Modern irrigation devices, each capable of spraying million liters of water a day, have produced a landscape dominated by geometric patterns of circular green islands of crops.162. This unprecedented development of a finite groundwater resource with an almost negligib。 this depends on the sizes of the individual cavities and the crevices linking them.122. Much of the water in a sample of watersaturated sediment or rock will drain from it if the sample is put in a suitable dry place.123. It is held there by the force of surface tension without which water would drain instantly from any wet surface, leaving it totally dry.124. The total volume of water in the saturated sample must therefore be thought of as consisting of water that can, and water that cannot, drain away.125. If the pores are large, the water in them will exist as drops too heavy for surface tension to hold, and it will drain away。 if they are now below the water’s upper surface (the water table), the gravels and sands of the former riverbed, and its sandbars, will be saturated with groundwater. 120. This is because the gaps among the original grains are often not totally plugged with cementing chemicals。 this is the groundwater that circulates as part of the water cycle.112. At first thought it seems incredible that there can be enough space in the “solid” ground underfoot to hold all this water. 113. The monest spaces are those among the particles—sand grains and tiny pebbles—of loose, unconsolidated sand and gravel.114. Beds of this material, out of sight beneath the soil, are mon.115. They are found wherever fast rivers carrying loads of coarse sediment once flowed.116. The water was always laden with pebbles, gravel, and sand, known as glacial outwash, that was deposited as the flow slowed down.117. The same thing happens to this day, though on a smaller scale, wherever a sedimentladen river or stream emerges from a mountain valley onto relatively flat land, dropping its load as the current slows: the water usually spreads out fanwise, depositing the sediment in the form of a smooth, fanshaped slope.118. Sediments are also dropped where a river slows on entering a lake or the sea, the deposited sediments are on a lake floor or the seafloor at first, but will be located inland at some future date, when the sea level falls or the land rises。crow’s feet wrinkles around the eyes and a subtle drop in the eye cover fold so that the skin above the eye moves down slightly toward the eyeball, can lead to pleasant feelings103. Ekman’s observation may be relevant to the British expression “keep a stiff upper lip” as a remendation for handling stress. It might be that a “stiff” lip suppresses emotional response as long as the lip is not quivering with fear or tension.104. Hills and mountains are often regarded as the epitome of permanence, successfully resisting the destructive forces of nature, but in fact they tend to be relatively shortlived in geological terms.105. Lower mountains tend to be older, and are often the eroded relics of much higher mountain chains.106. Some mountains were formed as a result of these plates crashing into each other and forcing up the rock at the plate margins.107. Other mountains may be raised by earthquakes, which fracture the Earth39。 and the loss of independence that came with it.90. Nor did the Whigs envision any conflict in society between farmers and workers on the one hand and business people and bankers on the other.91. Religion and politics, they believed, should be kept clearly separate, and they generally opposed humanitarian legislation.92. Whigs appealed to planters who needed credit to finance their cotton and rice trade in the world market, to farmers who were eager to sell their surpluses, and to workers who wished to improve themselves.93. Neither party could win an election by appealing exclusively to the rich or the poor.94. Democrats attracted farmers isolated from the market or unfortable with it, workers alienated from the emerging industrial system, and rising entrepreneurs who wanted to break monopolies and open the economy to newers like themselves.95. The Whigs were strongest in the towns, cities, and those rural areas that were fully integrated into the market economy, whereas Democrats dominated areas of semisubsistence farming that were more isolated and languishing economically.96. The Fore also displayed familiar facial expressions when asked how they would respond if they were the characters in stories that called for basic emotional responses.97. Ekman and his colleagues more recently obtained similar results in a study of ten cultures in which participants were permitted to report that multiple emotions were shown by facial expressions.98. The facialfeedback hypothesis argues, however, that the causal relationship between emotions and facial expressions can also work in the opposite direction.99. The free expression by outward signs of an emotion intensifies it. On the other hand, the repression, as far as possible, of all outward signs softens our emotions.100. Causing participants in experiments to smile, for example, leads them to report more positive feelings and to rate cartoons (humorous drawings of people or situations) as being more humorous.101. Selfperception of heightened arousal then leads to heightened emotional activity. Other links may involve changes in brain temperature and the release of neurotransmitters (substances that transmit nerve impulses.)102. Ekman has found that the socalled Duchenne smile, which is characterized by 39。 the plex dealing。s aesthetic intentions, pla