12. Hesperorthis tricenaria, Brachiopod, Middle Ordovician (Black River and Trenton Stage). Interior view of the pedicle valve.
Fig. 5. The surface of a layer or bed of Glens Falls Limestone. Pen points to a colonial Bryozoan Prasopora “head.” These “heads” are very common just south or to your left if walking down the ramp.
Brachiopods. Brachiopods are abundant in the Park rocks (see [Plate 1], 4A, B; 5; 6; 9; 10; 11; 12). These invertebrates are small marine animals which generally live in waters no deeper than 600 feet. The two valves of their shell are joined at the back (posterior) end of the body along a hingeline of interlocking teeth and sockets. The shell of the brachiopod is opened or shut by muscles attached to the inside of each valve. Brachiopods are found in the oldest rocks containing definite and abundant fossils. Brachiopods are still living today.
Bryozoans. Bryozoans or “moss animals” are very small marine animals which live in colonies. The bryozoans construct their mutual home or colony of lime which is commonly preserved for the fossil record. Large colonies of the fossil Prasopora (prah-sop-OR-ah) are commonly seen on the weathered surfaces of many of the rock layers in the Park (see [Plate 1]; 7A, B, C; 8 and [Figure 5]). Individuals of one genus common here, can be recognized by their chocolate drop shapes. Bryozoans first appear in lower Paleozoic rocks and are still living today in clear well-circulated shallow to deep marine water. Considering all of the fossils found in the Park rocks, the past environment is thought to have been a relatively shallow and warm sea.
Fig. 6. This photograph shows the typical thickness of the Glens Falls Limestone beds in the Park area. Note the massive nature of the limestone bed. The 5-inch pen in the center of the picture is for scale.
Fig. 7. Sections illustrating the geologic history of D.A.R. State Park.