Plates— Page 1. Geologic time scale Frontispiece 2. Types of fossil preservation 8 3. Silicified brachiopods dissolved from Permian limestones of the Glass Mountains, Brewster County, Texas 12 4. Dinosaur tracks in limestone in bed of Paluxy Creek near Glen Rose, Somervell County, Texas 15 5. Fossil collecting equipment 18 6-8. Fossil identification charts 28-30 9. Physiographic map of Texas 36 10. Geologic map of Texas 38-39 11. Geologic range of the major groups of plants and animals 45 12. Fossil plants—thallophytes and tracheophytes 46 13. Fossil plants—tracheophytes 47 14. Paleozoic sponges and sponge spicules 51 15. Pennsylvanian corals 52 16. Cretaceous and Tertiary corals 53 17. Pennsylvanian bryozoans and Cambrian and Mississippian brachiopods 55 18, 19. Pennsylvanian brachiopods 57, 58 20. Pennsylvanian gastropods 61 21. Pennsylvanian and Cretaceous gastropods 62 22, 23. Tertiary gastropods 63, 64 24. Pennsylvanian pelecypods 67 25-28. Cretaceous pelecypods 68-71 29-31. Tertiary pelecypods 72-74 32. Pennsylvanian and Cretaceous cephalopods 76 33. Cretaceous cephalopods 77 34. Fossil arthropods 79 35. Fossil starfishes, crinoids, and holothurian sclerites 83 36. Cretaceous echinoids 84 37. Primitive armored fish, shark teeth, and conodonts 88 38. Comparison of the dinosaurs 90 39. Comparison of Mesozoic flying and swimming reptiles 91 40. Pelycosaur, cotylosaur, and a primitive amphibian 92 41. Swimming reptiles 93 42. Phytosaur and flying dinosaurs 94 43. Skull of _Phobosuchus_, from Cretaceous of Trans-Pecos Texas 96 44. Saurischian dinosaurs 98 45. Ornithischian dinosaurs 99 46, 47. Cenozoic mammals 101, 103 48. Tertiary mammals 105 49.