[1]The granite found in Darling State Park is white or pinkish in color
and most times is speckled with shiny black mica flakes. On close
inspection, grains of smoky to clear color are seen within the rock.
The white and pink grains are the mineral, feldspar; the shiny black
flakes, biotite mica; the smoky to clear grains, quartz or silica. A
magnified picture of a slice of granite (see Fig. 2) shows the
individual mineral grains and their interlocking nature with each
other. Granite belongs to a major family of rocks, termed _Igneous
rocks_. Igneous rocks are formed through the hardening or
lithification of molten rock-material when subjected to the cooler
temperatures at or near the earth’s surface. The molten rock
material formed at some depth beneath the surface of the earth,
where temperatures were many hundreds of degrees hotter than at the
surface.
[2]Metamorphic rocks are either sedimentary (this, a third major family
of rocks which is characterized by a layered appearance that has
been retained by many of the altered park rocks) or igneous rocks
(the granite) which have been under the influence of pressure, heat,
and chemically active fluids, oftentimes resulting in chemical and
structural changes. Most of the metamorphic rocks seen in the park
are either schist, phyllite, slate or quartzite. For the benefit of
the more advanced student, the rocks of the park area are considered
a granite-hornfels complex (see Bertram G. Woodland’s paper of 1963,
“A Petrographic study of Thermally Metamorphosed Pelitic rocks in
the Burke Area, Northeastern Vermont,” in the American Journal of
Science, volume 261, pages 354 to 375).
[3]Sedimentary or layered rocks, the third major rock family, are
composed of pieces, grains and other materials from older
metamorphic, igneous and sedimentary rocks. These fragments have
been carried by rivers and streams to some resting place at the
bottom of a sea, lake, or stream channel. This mud, sand and gravel,
under the weight of steadily increasing overburden, and the presence
of cementing materials, slowly hardened into rock which we now call
limestone shale, sandstone, and conglomerate.
[4]A geologic formation consists of a sequence of rock layers which were
deposited under essentially the same conditions, or a series of
alternating conditions, and which can be easily distinguished and
mapped as a unit by geologists in the field.
[5]Geologic time is divided into four Eras which are designated from
oldest to youngest: Precambrian, Paleozoic, Mesozoic, and Cenozoic.
Each of these Eras is divided into geologic periods of time. The
Devonian Period is in about the middle of the Paleozoic Era and
began some 330 million years ago and ended approximately 290 million
years ago (see Geologic Time Scale, Fig. 14).
[6]A joint is a break in a rock mass which interrupts its physical
continuity. A group of more or less parallel joints is known as a
joint set.