[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.
