They are phyla, Brachiopoda, characterized by a food-catching organ called a lophophore and a bilaterally symmetrical shell. Individual chert pebbles often exhibit the cross-section of the spiralium where a brachiopod shell has been worn down by erosion. Some have the form of a garden trellis. The partitions in the shells strengthen the shells. Also, the partitions formed chambers that contained gas that cephalopods use to control their buoyancy as they swam through the seas.
Cephalopods are generally very rare fossils within the chert gravels.
Corals - Corals are marine invertebrates that belong to the Phylum Anthozoa which also include sea anemone and jellyfish. Corals, as they are in modern seas, were also reef builders in the warm shallow seas that covered large parts of North America. Two types of corals, tabulate and rugose corals occur within the chert gravels. Tabulate coral consists of numerous tightly packed corallites, which exhibit a fine polygonal pattern when viewed from the top. When viewed from the side, they look like a bunch of straight tubes with numerous partitions perpendicular to the sides of the tubes.