GRE Reading Comprehension
Volcanic rock that forms as fluid lava chills rapidly is called pillow lava. This rapid chilling occurs when lava erupts directly into water (or beneath ice) or when it flows across a shoreline and into a body of water. While the term "pillow lava" suggests a definite shape, in fact geologists disagree. Some geologists argue that pillow lava is characterized by discrete, ellipsoidal masses. Others describe pillow lava as a tangled mass of cylindrical, interconnected flow lobes. Much of this controversy probably results from unwarranted extrapolations of the original configuration of pillow flows from two-dimensional cross sections of eroded pillows in land outcroppings. Virtually any cross section cut through a tangled mass of interconnected flow lobes would give the appearance of a pile of discrete ellipsoidal masses. Adequate three- dimensional images of intact pillows are essential for defining the true geometry of pillowed flows and thus ascertaining their mode of origin. Indeed, the term "pillow," itself suggestive of discrete masses, is probably a misnomer.
Which of the following is a fact presented in the passage?
- A The shape of the connections between the separate, sack like masses in pillow lava is unknown.
- B More accurate cross sections of pillow lava would reveal the mode of origin.
- C Water or ice is necessary for the formation of pillow lava.
- D No three-dimensional examples of intact pillows currently exist.
- E The origin of pillow lava is not yet known.
Correct Answer: C