If the visitor confines his wanderings to the State Park the most conspicuous geological features, or clues to the Park’s past history, are concentrated in the clay banks and adjacent beach which border Lake Champlain (see [Fig. 4]). The clays which cover the entire Park record thousands of years of rather recent events, geologically speaking[5], which took place in the Champlain Valley. These clays also record a very significant phase in the development of present Lake Champlain. Before discussing the clays it will be necessary to outline some of the geological events which preceded the deposition of the clays, that is, some of those events which took place as the last glacial ice lobe slowly retreated up the Champlain Valley and into Canada. The author has borrowed heavily from an article by Donald H. Chapman entitled “Late-Glacial and Post-glacial History of the Champlain Valley” which was published in the 1941-1942 “Report of the State Geologist on the Mineral Industries and Geology of Vermont, twenty-third of (the) Series.”
Figure 3. Water-worn concretions seen on the beach of Button Bay State Park. The button-mold shape of some concretions led to the incorporation of the word “Button” in the name Button Bay (Originally, Button-Mould Bay). The chisel portion of the Alpine ice ax head is about 5 inches long.
During the final retreat of the last ice sheet to invade the New England states (some 11,000 to 12,000 years ago) an ice lobe, which occupied the Hudson-Champlain Valley, slowly wasted northward toward the Canadian border. Melt-water derived from the melting glacial ice together with atmospheric water (rain and snow) formed a succession of lakes dammed on the north by the glacial ice. These lakes emptied to the south through the Hudson Valley. This succession of lakes and intermediate lake stages will be discussed in the following paragraphs.
Figure 4. View of beach, Button Bay State Park, looking toward the southeast. The beach demonstrates several water-level and storm-level debris lines. Note the conspicuous lack of sand on this “clay” beach.
The oldest lake recognized by the geologists is termed “Lake Albany” and was confined to the Hudson Valley. At this time the area of present-day Lake Champlain, north of the Hudson Valley, was still covered by glacial ice which was slowly melting as the general regional climate throughout New England became warmer and warmer. Soon the whole Hudson Valley region began to rise[6] out from beneath the lake waters and “Lake Albany” shallowed. Eventually a rock ledge emerged just south of Schuylerville, New York (actually at Coveville, New York) over which the waters from a new lake, Lake Vermont, began to flow.
Lake Vermont, with its rock ledge dam at Coveville, began to expand northward as the ice front retreated up the Champlain Valley. Several distinct stages in its development are now recognized in features[7] demonstrating past lake levels which are abundantly displayed close to Button Bay State Park. The “lake-level indicators” or features tell us, in addition to the number of distinct lake stages in a given area, something about past earth movements. A “line of lake-level-elevation”[8] is drawn through those features outlining each past lake or lake stage followed by a comparison of each line with those lines constructed for older and younger lakes or lake stages. If, for any two lake-level lines compared, these lines are not parallel, it can be assumed that the earth’s crust was tilted during the time between the formation of their lake-level features. This idea of tilting of the earth’s surface, which is supported through the study of successive lake levels, has proven the key to the present status of Lake Champlain.
At the beginning of its history Lake Vermont emptied to the south through an outlet channel located in the vicinity of Coveville, New York (see map, [Fig. 5]A). This stage in the development of Lake Vermont, often referred to as the Coveville Stage, saw lake waters fill the Champlain Valley from the Green Mountains on the east to a position west of the present New York-Lake Champlain shoreline. Such Vermont towns as Middlebury, Vergennes, Hinesburg, Burlington and Colchester would have been submerged beneath the lake waters (see map, [Fig. 5]B). Certain high areas such as Mount Philo, Pease Mountain and Cobble Hill show lake-level features along their sides which prove that these areas were islands rising above the level of this past lake. If you visit Mt. Philo State Park, located approximately 11 miles north of Vergennes, one of these lake-level features, a wave-cut terrace, can be seen at an elevation of 545 feet and on the south side of the hill (at the level of the second reverse turn in your trip to the summit area).[9]
