[1]A rock, for those desiring a more technical definition, is any
relatively hard, naturally occurring, combination of minerals which
form an essential part of the earth. Minerals are composed of one or
more chemical elements, such as oxygen or silicon, that form in
nature.
[2]A fault is a break or fracture in the rocks of the earth’s crust
where one side of the fracture moves in some direction relative to
the other side. Some recent earthquakes in California and Nevada
have produced visible faults where, for instance, roads were cut and
one side displaced several yards from the other.
[3]Most of the mineral grains which make up a schist, a metamorphosed
shale or sandy shale, can be seen with the naked eye, and the
parallel to subparallel arrangement of platy or flaky minerals, such
as the abundant mica, is the most obvious feature. In bright
sunlight a schist presents a very shiny, almost silvery appearance
which is caused by the reflection of sunlight from the many parallel
mica plates. A phyllite has much the same mineral composition as
that of a schist; however, the individual mineral grains are too
small to be seen without the aid of a magnifying glass. As with the
schist, a phyllite when viewed in direct sunlight, appears shiny.
Quartzites are metamorphosed sandstones which have been fused into
great hardness through the application of heat and pressure.
[4]A geologic formation consists of a group of similar rocks, or
sequence of rocks, which can be easily distinguished from adjacent
rocks and whose distribution can be plotted on a map.
[5]More technically this schist is termed a chlorite-sericite-quartz
schist.
[6]The geologist divides geologic time into four major sections,
designated Eras. These Eras are in turn subdivided into Geologic
Periods which are of shorter time duration. The Cambrian Period is
the oldest of the Paleozoic Era and began some 550 million years
ago. The Ordovician Period is the next oldest of the Paleozoic Era
and started about 440 million years ago and ended close to 360
million years ago.