|This next page on the invertebrate fauna only contains the most common invertebrates that are found here. This invertebrate fauna is so extensive that some New Jersey paleontologists have specialized in studying it. Most are found in situ downstream from the Hillsdale Road bridge in the Navesink formation. Most of the invertebrates that are found upstream from Boundary Road bridge are represented only as molds and casts. This occurred because the original shell material was leached away by ground water. In the less permeable Navesink at Big Brook, only the shells made of argonite were leached away, while the shells made of calcite remained.