Chapter II: The Earliest Known Vertebrates

Methods of interrogating Nature, 18; thickness of sedimentary
rocks, 20; earliest traces of life, 21; early vertebrates
difficult of preservation, 22; armored fishes, 23; abundance of
early fishes, 25; destruction of fish, 26; carboniferous sharks,
29; known mostly from teeth and spines, 30; references, 32.