Part 1

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. 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’ 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.”

Why the name Button Bay? H. M. Seely (1910, p. 274) when discussing the shoreline of this bay states, “Besides shells, concretions, 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, 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.”

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.

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 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 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” 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).

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.

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.

The conspicuous clays of Button Bay State Park were deposited during the next episode in the history of the Champlain Valley, a development heralded by continued retreat of the ice lobe and contact with the St. Lawrence marine waters. Let’s take a look at the clays so well displayed along the Button Bay State Park beach and see if we can piece together their history.

THE CLAYS OF BUTTON BAY STATE PARK

The best location in the park for a good look at the clays which cover the entire Park area is along the lake beach (see Figs. 4 and 8). The bank averages 23 feet in height measured from the beach to the top of the bank. The width of the beach varies seasonally and during storms as the water level of Lake Champlain fluctuates (see Figs. 4 and 8). A walk along the beach will reveal some interesting facts about the composition of the beach and the adjacent clay banks.

One cannot help observing the scarcity of sand on the beach. The only adjacent material to build this beach is clay, which here contains a small quantity of sand and some concretions containing lime. The sickle shape of Button Bay keeps most foreign sand from the beach. The small patches of sand present soon give way to blue clay which, in many places, forms the base of the beach. This blue clay can also be seen in the base of the bank in the southern portion of the Park, where it underlies and is therefore older than the brown clay.

Actually very little of the blue clay is exposed in the Park. From other locations along the shore of Lake Champlain and in the more inland areas of the Champlain Lowlands geologists have found many clues to help our understanding of its history.

In August 1849 the incomplete skeleton of a whale was found in a railroad cut being excavated for the Rutland and Burlington Railroad. This cut was located approximately 12 miles south of Burlington and a mile east of Lake Champlain. The significant fact about this “find” is that these bones were found in the same type of blue clay that occurs at the beach in Button Bay State Park. Clam and oyster shells (Pelecypods) were found in association with the whale bones. These pelecypod shells and the whale bones show that these animals lived and died in cold marine waters. Lake Champlain today is a fresh-water lake and the fish and other organisms in it are those of fresh, not salty water. Yet the blue clays (and we are soon to learn, the brown clays) hold evidence proving the existence of sea water in an area where a fresh-water lake is found today. Can this be explained?

The brown clay forms most of the Park’s clay banks (see Figs. 9A and 9B ). It can be examined easily by the visitor. The bank is composed of clay and variable amounts of fine sand in thin lens-shaped bodies. The hard dry outer clay, if rain has not just fallen, of the upper 15 feet of the bank appears light brown or tan-white and commonly contains interspersed white and blue streaks. In the section of the bank which was the object of detailed study, two conspicuous convoluted beds were found, one 5 feet above the beach, the other nearly 2 feet above the first.