The Geology of Button Bay State Park

THE OLDER ROCKS

The rocks which underlie Button Bay State Park can be seen along the small creek which is located just south of the Park. It is suggested that the visitor walk southward (to the right if approaching the road from the lake front) along the main park road until the first culvert beneath the road is reached. Looking down the creekbed toward the lake, one can readily see the older rocks (see A, Figure 11). Fossils[18] are found in these tilted rocks which tilt or dip toward the northeast and “strike” northwestward. Fossils date the rocks underlying Button Bay State Park as Middle Ordovician.[19] The most abundant fossil is a trilobite, Triarthrus, but, even this ancient arthropod[20] is not easily found in these limestones and limy shales. A sketch of Triarthrus (that portion found fossilized) appears in Plate 1. These rocks containing Triarthrus beckii belong to the Stony Point formation and are of late Sherman Fall or Denmarkian age.

One of the jobs of the geologist is to reconstruct the paleogeography (ancient geography) of a region. The different kinds of rocks present and their distribution patterns, together with the types of fossil plants and animals found, tell the geologist of past lands and seas, warm and cold climates. The rocks of the Stony Point formation (the rocks which underlie most of the Park) tell of warm marine waters, a past sea, bordered by relatively low land areas. The fossils contained in the Stony Point formation attest to the presence of relatively shallow marine waters. The fact that these Ordovician rocks are tilted and broken by faults proves that major earth movements[21] took place sometime after their lithification.

PLATE 1

1A, B, C; Maclurites magnus Lesueur (X 0.5). Lower, upper and side views. Crown Point limestone. GASTROPOD (snail).
2; Triarthrus beckii Green (X 3). Top view of central part of head region. Stony Point shale. TRILOBITE.
3; Saxicava (X 3). Pleistocene marine clays. PELECYPOD.
4; Macoma (X 3). Pleistocene marine clays. PELECYPOD.
5A, B; Rhinidictya (X 9 and X 1). Orwell limestone. BRYOZOAN.
6A, B, C: Cryptolithus tesselatus Green (X 2). Top, side and front views. Glens Falls limestone. TRILOBITE.
7; Rafinesquina. Internal view. Orwell and Glens Falls limestones. BRACHIOPOD.

FIGURE 11 GEOLOGIC MAP OLDER ROCKS

(fault)
CROWN POINT LIMESTONE
CHAZY (VALCOUR?) (Clay covered in most areas)
ORWELL LIMESTONE (clay covered)
GLENS FALLS LIMESTONE (clay covered in most areas)
(fault)
STONY POINT FORMATION (clay covered in most areas): GEOLOGY NORTH OF PARK BOUNDARY ADAPTED FROM CHARLES W. WELBY—1961

From the north boundary of the Park and along the Lake Champlain shoreline older and older Ordovician rocks are encountered.[22] The rocks (see geologic map, Fig. 11), primarily tilted marine limestones, display a variety of fossils, some of which are illustrated in Plate 1. Figure 12 is a view of the west side of Button Island showing an 18-inch thick reefy zone in the Orwell limestone. The reefy zone is composed largely of tumbled heads of colonial corals and stromatoporoids. A selected list of reference books and articles, some of which contain plates picturing Ordovician fossils, is found at the end of this section.

Ordovician and older rocks were lifted, folded and faulted during the Taconic Disturbance. Dramatic evidence for this period of crustal instability is seen in the Champlain Thrust, a major series of faults which can be seen east of Button Bay State Park. The evidence for such a fault system, which is more fully discussed in another pamphlet, is readily seen on Mount Philo where older Cambrian rocks have overridden (been thrust over) younger Ordovician ones.

As time passed in the Button Bay region younger and younger sediments were deposited over the top of folded and eroded Ordovician rocks. These sediments became rock and in turn slowly broke into fragments which were transported to other areas where they were deposited again as sediments. The glaciers passed over, leaving their rock debris behind as they wasted northward. Marine clays were slowly deposited from the waters of the Champlain Sea. Today only the marine clays resting on the beveled edges of Middle Ordovician rocks can be seen in the Park.

The history of the earth is open for all to read. Button Bay State Park can tell us only the history which is recorded in its clays and underlying rocks. As we have seen, there are certain giant geologic time gaps in the Park area, but many of these do not exist in other places and in other Parks. If this pamphlet has stimulated an interest in filling in these time gaps through your study of rocks in other places, then it has fulfilled its purpose. The present interest in Space demands a good long look at the Planet Earth. Good Hunting!

Figure 12. Bedded Orwell limestone on open-lake side of Button Island, showing patches of stromatoporoids and colonial corals (white areas). Photo by C. W. Welby.

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