Almost all of the boulders deposited by the glacier are composed of white granite similar to the rock which underlies the entire area. This indicates that most of the boulders have not been transported very far. However, occasionally boulders are found which are not characteristic of the area and represent rocks brought in from the north. Such boulders which are foreign to the area in which they are found are called _erratics_. Most erratics in this area are dark-colored metamorphosed rocks in which the minerals are oriented to give the rock a layered pattern. These are called either _gneisses_ or _schists_ depending on whether the layering is coarse or fine. Deposits of the glacier are exposed in two gravel or sand pits near the Stillwater Camp site. These deposits are composed principally of sand but contain scattered boulders of different sizes. A few erratics are found in these deposits—particularly a variety of rock which weathers to a soft, brown porous mass resembling decayed wood. These sandy deposits probably were plastered onto the ground from the sole of the creeping glacier or were simply let down as the glacier wasted away. Because of the irregular manner in which the glacier may deposit its load of sand and gravel, the topography in such areas is uneven and characterized by poor drainage. At a number of places in Groton swampy areas occur at higher elevation which might normally be expected to be well-drained. Some of these areas have become the sites of beaver dams because they are ideal for damming up the water. GEOLOGY OF NEARBY AREAS _Ricker Mills_ Just south of the park at Ricker Mills some of the oldest rocks in the area are exposed in the railroad cut just north of the highway crossing. These rocks belong to a thick sequence of similar rocks which are collectively called the _Waits River formation_. Studies in other areas indicate that these rocks belong to the portion of geologic time called the Ordovician period which was more than 350 million years ago.