[7]As the ice retreated, a succession of lakes formed in the Champlain Valley. Each lake had a level waterline during its history and certain lakeshore features formed, as they do in any present-day lake, with respect to each past level water-line. For example, ridges of sand and gravel were heaped along the shoreline by lake waves. Wave-cut and wave-built flat areas or terraces were formed along the margins of lakes or along the sides of islands within a lake. Streams entering a lake built deltas by depositing materials it had carried down from the surrounding highlands. [8]Elevation is measured in feet above the mean sea level of today, with mean sea level being zero feet. [9]A most impressive view can be gained from any one of the several lookout points at the summit level of Mt. Philo. Looking to the west, toward Lake Champlain, and south in the direction of Vergennes and Button Bay State Park, a three dimensional view of an old lake (Lake Vermont) can be seen. In this view the present Lake Champlain Lowlands represent the old lake bottom and the numerous hills rising above this Lowland were once islands or near-islands which dotted the surface of the lake. It takes very little imagination to place yourself on the “island of Mt. Philo” and to visualize a boat tied to a dock just below the rocky cliffs on which you stand. A trip to Mt. Philo with its spectacular view of the Champlain Lowlands (see Fig. 6) is recommended. [10]One word of caution, the Park authorities may import sand from other areas of Vermont to improve the swimming facilities along the beach. In this case, the abundant sand on the beach will not constitute the “natural beach composition” for Button Bay State Park. [11]The blue color is due to the presence of ferrous iron (bivalent iron) together with iron compounds in which iron has its higher chemical valence (ferric iron). This ferrous iron demands a chemically reducing environment for its formation and indicates that the clays were deposited in a shallow sea or that they remained for some time beneath a stable water-table. They contained a fair quantity of decaying organic material. [12]The brown color is due to the presence of the ferric hydroxide, goethite (HFeO₂). [13]This fossil whale is scientifically known as _Delphinapterus vermontanus_ (_Thompson_). [14]The pelecypods found are scientifically known as _Macoma groenlandica_ and _Saxicava rugosa_. [15]The size limits of sand lie between 2mm in diameter (largest) and ¹/₁₆mm in diameter (smallest). Two millimeters (mm) equals approximately ²/₂₅ inches. Fine sand would fall between ¼mm and ⅛mm in diameter.