This field trip will focus on the petrology and structure of basementcored anticlines in the central Appalachian Piedmont, near Baltimore, Maryland (Figure 1). These structures have long been interpreted as mantled gneiss domes in the sense of Eskola (1949). However, recent work suggests that they are recumbent nappes, arched by later folding about steeply dipping axial planes. <...>

There are three categories of rocks- igneous, sedimentary and metamorphic. Igneous rocks have been formed by solidification of hot silicate melts known as magmas, which may be erupted at the Earth's surface as lavas from volcanoes. Sedimentary rocks form by a variety of processes at low temperatures near the surface, including the bottom of the seas and oceans. Metamorphic rocks, the third category, were originally either igneous or sedimentary, but their character has been changed by processes operating below the surface of the Earth. The constituent minerals of the rocks may be changed, or the shapes, sizes and mutual spatial relationships of the crystals may change. There are a variety of processes involved, and they are collectively described by the term metamorphism. <...>

Sediments are formed of materials deposited episodically from water, air and ice, as well as soils, coals and volcanic detritus. Compaction, cementation and burial processes lithify loose sediments into sedimentary rocks and occasionally mask the character of the original deposit. Fortunately, many lithified rocks possess qualities so similar to those of modern deposits.that the conditions under which they formed can be determined with some certainty. When fossil remains and traces exist, such determinations are greatly facilitated. On the other hand, there are sedimentary rocks, such as banded iron-formations and chalks, which can be described accurately but which still defy completely satisfactory genetic interpretation, because there are no clear modern equivalents. <...>

Leaving aside the atmosphere and hydrosphere, rocks are the stuff of which the earth is made. Because of this, the study of rocks, petrology (from the Greek petra, “rock,” and logos, “discourse or explanation”), occupies a central position among the earth sciences. The study of rocks is the source of virtually all of our ideas about the history of Earth. Knowledge about rocks, their origin and ages, and their distribution is potentially capable of contributing to the solution of a wide variety of problems that run the gamut of geological interests.