Cover Picture: Selected “buttons” from the clay bank along the beach at Button Bay State Park. (×0.8).

THE GEOLOGY OF BUTTON BAY STATE PARK

By HARRY W. DODGE, JR.

DEPARTMENT OF FORESTS AND PARKS Perry H. Merrill, Director

VERMONT DEVELOPMENT DEPARTMENT

VERMONT GEOLOGICAL SURVEY Charles G. Doll, State Geologist

1962

THE GEOLOGY OF BUTTON BAY STATE PARK

By Harry W. Dodge, Jr.

INTRODUCTION

Button Bay State Park is located on the eastern shore of Lake Champlain with lake frontage on Button Bay (see maps, Figs. 1 and 2). This Vermont State Park is reached from the nearest large town, Vergennes, by proceeding southwest, toward Addison, on State Route 22A for .25 miles beyond the bridge over Otter Creek, thence, right on the Basin Harbor-Panton road for another 1.4 miles to the first road entering from the right. Turn right on this, the Basin Harbor road, and proceed for 4.5 miles, thence, left for 1.4 miles to Button Bay State Park (see map, Fig. 2, note arrows). A more direct road is planned to connect the Basin Harbor Road with the Park, however, this route has still not been completed.

Prior to its present name, Button Bay, the “sickle-shaped bay” on which Button Bay State Park is located was termed Button Mould Bay[1]. In “The Journal of William Gilliland” which is found in the “Pioneer History of the Champlain Valley” by Winslow C. Watson, Albany, 1863, and under the date of September 7, 1765, is found an entry which speaks of “his (Gilliland) overtaking ‘the Governors and other gentlemen’[2] at Button Mould Bay, and going aboard their sloop.”

A book of charts by Captain William Chambers contains one entitled “Baye du Roche Fendue (Split-Rock Bay) and the soundings taken in August 1779.” At the upper corner of the chart is the name “Button Mould Bay.” The first appearance of the shortened version, Button Bay, seems to be in Whitelaw’s map of 1796 which was used as the frontispiece of the Census volume, “Heads of Families, Vermont, 1800.”

FIGURE 1 MAP OF WEST-CENTRAL VERMONT AND EASTERN NEW YORK

FIGURE 2

Why the name Button Bay? H. M. Seely (1910, p. 274)[3] when discussing the shoreline of this bay states, “Besides shells, concretions[4], some of strange imitative forms (many shaped like animals), are loosened from the clay.” He goes on to say that a “form particularly abundant in the banks of the bay (and on the beach) has the shape and size of a turned wood button-mold (mold is commonly spelled ‘mould’ by the British), a disc with a hole in the center, plane (flat) on one side and convex on the other” (see Fig. 3 and cover picture). The abundance of these button mold-shaped concretions obviously led to the older name, Button Mould Bay which was later shortened to Button Bay.

THE GEOLOGY OF BUTTON BAY STATE PARK

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 7 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 9 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. 5A). 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. 5B). 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]

FIGURE 5 EARLY COVEVILLE MAXIMUM COVEVILLE

Figure 6. Looking west from the top of Mount Philo State Park. The Adirondack Mountains are on the skyline, Lake Champlain in middle background and the Champlain Lowlands stretch from Lake Champlain to the base of Mount Philo.

FIGURE 7 FORT ANN MAXIMUM MARINE MAXIMUM

Shortly after Coveville Lake Vermont reached its maximum size (see map, Fig. 5B), a southern gorge-outlet was formed at an elevation lower than the previous Coveville outlet in the vicinity of Fort Ann, New York (Fort Ann is located approximately 8 miles south of the present southern extremity of Lake Champlain). The level of Lake Vermont’s water dropped to the new Fort Ann Stage (see map, Fig. 7A). Evidence for this new lake level is seen on the slopes of Mt. Philo, Snake Mountain and Cobble Hill. These lake-level features are parallel to and found 100 feet below those of the Coveville Stage. These parallel features, then, indicate that very little, if any, tilting of the earth’s crust had taken place between the Coveville and Fort Ann lake stages.

Figure 8. Beach and clay banks exposed along the Lake Champlain portion of Button Bay State Park. This view is toward the northwest and includes a major portion of the Park’s lake frontage. Photo by Robert B. Williams.

This Champlain ice lobe continued to melt and retreat toward the Canadian border and beyond. As the glacial front approached the St. Lawrence valley, fresh water from Lake Vermont began to seep through the retreating ice lobe and into the marine waters which filled the St. Lawrence area. Several shoreline (lake-level) features are found at different elevations below the Fort Ann Stage of Lake Vermont and attest to a slow lowering of the lake level by the escape of fresh water to the north.