The geologist uses the terms dip and strike to describe foliation and uses conventional symbols for plotting purposes (See geologic map). The dip of the foliation is the angle between an imaginary horizontal line and the tilt or downward slope of the foliation. The strike is the compass direction of a line formed by the dipping foliation plane and its intersection with an imaginary horizontal plane (See block diagram, Fig. 2). A glance at the geological map will show that the rocks of the Park area consistently strike north to northwest and dip to the east. If you look at the foliation symbols which are plotted on the geologic map, the straight line of the symbol indicates the strike and the black triangle points in the direction of the dip. The angles of dip have not been included on the map; however, they average forty-five degrees down from the horizontal and toward the east or right margin of the geological map. THE ROCKS OF CALVIN COOLIDGE STATE FOREST PARK AND THE STORY THEY TELL The rocks of Calvin Coolidge State Forest Park can be divided into four distinct units or _formations_[4]. The geologic map shows these formations as distinct bands, each band representing a different formation and its intersection with the ground surface. Each formation is, so to speak, stacked upon the next older with the oldest forming the western band and the youngest on the east. Remember that these metamorphic rock formations were originally sedimentary in nature and were deposited in a nearly horizontal position on the floor on an ancient sea. The fact that they are now tilted indicates that earth movements have taken place sometime after the sedimentary rocks hardened but before the present time. The _Pinney Hollow formation_, the oldest formation of rocks seen in the Forest Park, was named for the excellent exposures of this formation in Pinney Hollow, a valley located along the western border of Coolidge Forest. You can readily see this formation, in its most typical development, along State Highway 100A about three-tenths of a mile south of the Park entrance road. Here, a historical monument which commemorates the naming of Pinney Hollow, is embedded in this formation (See photograph, Fig. 3). The lean-to, tent platform and picnic areas are situated on this formation and its rocks are easily observed. It is interesting to note that some of the Pinney Hollow rocks seen in these camping and picnicking spots differ from the typical rocks seen along State Highway 100A. In fact, some of the rocks which are dark and are classed as phyllites, can be confused with the overlying Ottauquechee rocks. A transition zone, several hundred feet wide, exists between these two formations and in which the two distinct rock types are intermingled. This “mixture” zone indicates that there was no break in the original deposition of these two formations and therefore the rock record during this time is complete.