March 2010, but by the end of the year 18 states had filed or joined lawsuits chal-
lenging the authority of the federal government to enforce many of the provisions
of the law, claiming that the law violates the sovereignty of the states. Also in
2010, the state of Arizona passed a controversial law allowing the detention of ille-
gal immigrants by local law enforcement. In this case, the federal government has
sued the state of Arizona, arguing that the state has no authority to pass and
enforce laws governing immigration, which lies in the realm of federal authority.
Both of these cases will likely be resolved by the Supreme Court, illustrating that
in most federations, the power dynamic between centralized government and indi-
vidual territorial entities is often a matter of both debate and litigation.Folding and Faulting
Plate Tectonicsis explained later. It is clear by all evidence that Earth’s crust is
not permanently configured. Instead, the surface is moving with a shuffling of con-
tinents and creation and destruction of the crust over millions upon millions of
years. Within the panoply of effects resulting from plate tectonics is the striking
evidence that “solid rock” is not everlasting in its structure or position. Movements
within the crust are usually slow and hardly consistent. With careful study ofgeo-
morphology, some localized evidence of crustal rearrangement can be related to
larger scales while others seem to have very local sources. The crust is capable
of various contortions and two of the most important are folding and faulting
where the former refers to rocks bent from their original position and the latter
refers to rocks that have broken. Both folding and faulting are difficult to compre-
hend from usual human experience. Without machines, a human cannot apply the
correct pressure over a long enough time to fold rock. Similarly, humans perceive
rocks as hard substances that can be made to break if force is sharply applied with
a tool or an explosive. The natural processes apply huge forces over vast time and
rocks are quite capable of being bent or broken under these conditions. The term
diastrophism applies to this rearrangement of solid crust. Whereas some diastro-
phism can be explained by intrusion of molten material to cause surface distortion,
it is evident that most is not.
All sorts of forces might be applied in three dimensions to rock. Stress is force
applied over area. Stresses can be uniform from all directions and the stressed rock
will not permanently deform. However, there is often differential stress applied
from different directions and differential stress from a single direction. Three
types of stress are delineated. The first is shear stress in which forces are simulta-
neously applied from varying directions. The second is tensional stress that pulls122 Folding and Faulting