The marcellus shale
the marcellus shale is a black shale formation that was formed during the middle
devonian period. the shale extends from new york state as far south as alabama.
the marcellus shale is exposed at the surface in the northern finger lakes region, and
is buried 2.1 kilometers below the surface along the new york-pennsylvania border.
geologists estimate that the marcellus shale contains hundreds of trillions of cubic
feet of natural gas. most of the marcellus shale does not allow fluids (gases and liquids)
to flow through the rock. in order to obtain the natural gas trapped in the rock,
the shale is fractured. this hydraulic fracturing consists of drilling a well, then pumping
in large amounts of water containing chemicals and sand under high pressure to
create cracks in the gas-bearing rock. although this process can allow the trapped gas
to be removed from the shale, opponents of hydraulic fracturing argue that the
chemicals used in the process may lead to groundwater contamination.

the reading passage states, “most of the marcellus shale does not allow fluids (gases and liquids) to flow
through the rock.” this statement suggests that the marcellus shale is
(1) clastic
(2) coarse grained
(3) porous
(4) impermeable