Questions 34–44 are based on the following passage.
The Elements of Geology
by William Harmon Norton
Rocks exposed to the direct rays of the sun
(34) became strongly heated by day and expand. After sunset they rapidly cool and contract. When the difference in temperature between day and night is considerable, the repeated strains of sudden expansion and contraction at last become greater than the rocks can bear, and they break, (35) for the same reason that a glass cracks when plunged into boiling water.
[1] In cooling in the evening the surface shell suddenly contracts on the unyielding interior and in time is forced off in scales.
(36) [2] Rocks are poor conductors of heat,
(37) and hence their surfaces may become painfully hot under the full blaze of the sun, while the interior remains comparatively cool. [3] By day the outer (38) layer expands and tends to break loose from the mass of the stone.
[4] Many rocks, such as granite, are (39) made in grains of various minerals which differ in color and in their capacity to absorb heat, and which therefore contract and expand in different ratios. In heating and cooling these grains crowd against their
(40) neighbors, and tear loose from them, so that finally the rock disintegrates into sand. The conditions for the destructive action of heat and cold are most fully met in arid regions when vegetation is wanting for lack of sufficient rain. The soil not being held together by the roots of plants is blown away over large areas, leaving the rocks bare to the blazing sun in a cloudless sky. The air is dry, and the heat received by the earth by day is therefore rapidly radiated at night into space. There is a sharp and sudden fall of temperature after sunset, and the rocks, strongly heated by day,
(41) are effected and now chilled perhaps even to the freezing point. (42) In the cooling and crystallization process, magma undergoes a physical process that ends in igneous rock. (43) This could result in many disadvantages for future vegetation.
In the Sahara the thermometer has been known to fall 131 degrees F. within a few hours. In the light air of the Pamir plateau in central Asia a rise of 90 degrees F. has been recorded from seven o’clock in the morning to one o’clock in the afternoon. On the mountains of southwestern Texas there are frequently heard crackling noises as the rocks of that arid region throw off scales from a fraction of an inch to four inches in thickness, and loud reports are made as huge bowlders split apart. Desert pebbles
(44) is weakened by long exposure to heat and cold have been shivered to fine sharp- pointed fragments on being placed in sand heated to 180 degrees F. Beds half a foot thick, forming the floor of limestone quarries in Wisconsin, have been known to buckle and arch and break to fragments under the heat of the summer sun