This vertical movement of the fieldstones is not simply an artifact of soil erosion, it is the result of frost heaving. In the fall the soil freezes first beneath stones, because stones are a better conductor of heat than soil. Or, put another way, soil is a better insulator than rock in a sea of insulation, stones are chilly islands.

Because most glacial till has a fairly high water content, ice forms beneath fieldstones when they freeze, and the expansion of this ice forces them upward. Even when the ice thaws, the stones do not return to their original positions because during thawing particles of soil seep into the cavity beneath, partially preventing the stones from dropping. Like a ratchet on a car jack each freeze-thaw cycle gradually lifts the fieldstones toward the surface. Ina very cold winter there may actually be two thrusts per freeze. Ice expands when it initially forms, but as the temperature plummets, the ice contracts. In the reverse process, when this very cold ice finally melts, it must expand a second time, pushing the stone once more.

In theory, the upward movement of fieldstones should result in pure soil, all the stones above the frost line having been pushed to the surface and carried away. What a vision! Acres of pure, deep soil and crowbars rusting away unused. Alas, the fastest stones move only an inch or so a year, and most are orders of magnitude slower.

1. What does the passage mainly discuss?

(A) The effect of frost heaving on stones

(B) The water content of various types of soil

(C) Factors affecting the rate of ice expansion

(D) Seasonal variations in ground temperature

2. What statement was most probably made in the paragraph preceding this pasage?

(A) Pure soil is quickly eroded.

(B)  Fieldstones are lifted to the top of the soil.

(C)  It is not easy to move stones from fields.

(D) Ancient cultural artifacts are buried deep in the soil.

3. Where does the soil freeze first in the fall?

(A) On the tops of stones

(B) In areas of pure, deep soil

(C) Under rocks

(D) On islands

4. In the first paragraph, the author gives an example of

(A) glacier movement

(B) soil erosion

(C) climate change

(D) heat conduction

5. According to the passage, why do fieldstones remain raised in the soil when the ice thaws?

(A) Melting ice erodes the soil around them.

(B) Soil fills in under them

(C)  They remain in a frozen layer of topsoil.

(D) The frost line under which they are resting moves upward.

6. The author refers to a car jack in an analogy that illustrates how

(A) stones are pushed upward

(B) heavy rocks press down on deep levels of soil

(C) a crowbar is used to remove stones from soil

(D) automobile parts freeze in cold weather

7. Which of the following conclusions is supported by the third paragraph?

(A) Stones above the frost line will quickly be pushed upward.

(B) The number of stones surfacing each year is decreasing.

(C) Acres of pure, deep soil regularly result from frost heaving.

(D) New stones will continue indefinitely to surface at a slow rate.

8. In line14, the author exclaims "What a vision!" to express an attitude of

(A) fear

(B) disgust

(C) enthusiasm

(D) romance

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