9. _Sowerbyella_, Brachiopod, Middle and Upper Ordovician. Exterior view
of brachial valve. (X2)
10. _Rafinesquina_, Brachiopod, Middle and Upper Ordovician. Exterior
view of the pedicle valve.
11. _Platystrophia trentonensis_, Brachiopod, Middle Ordovician (Trenton
Stage). Anterior or front view.
12. _Hesperorthis tricenaria_, Brachiopod, Middle Ordovician (Black
River and Trenton Stage). Interior view of the pedicle valve.
[Illustration: 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.
[Illustration: 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.]
[Illustration: Fig. 7. Sections illustrating the geologic history of
D.A.R. State Park.]