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CHAPTER IV.
FROM THE LOWER EMIGRANT CROSSING OF THE RIO PECOS TO THE MOUTH OF DELAWARE CREEK.
May 12.-The greater portion of this day was spent in exploring the hills and cliffs in the vicinity of our camp on the Rio Pecos. The thickness of the Cretaceous Limestone here was estimated at not less than a thousand feet. In its lithological character it varies considerably from that previously encountered, consisting for the most part of hard, compact rock, often crystalline, and usually of a light bluish color. The greater portion of the mass is almost entirely destitute of organic remains, but near the summit of the highest hills I discovered a band of soft earthy limestone, of a bright yellow color, highly charged with elegantly preserved fossils, which have been determined by my brother, Dr. B. F. Shumard, to belong chiefly to the following species:
- Ammonites acuto-carinatus (Shum.),
- Ceratites (Ammonites) Pedernalis (Roem. sp.),
- Pterodonta subfusiformis (Shum.),
- Scalaria vertebroides? (Mart. sp.),
- Natica (Globiconcha) tumida (Shum.),
- Arcopagia Texana (Roem.),
- Panopoea Texana (Shum.),
- Janira quadricostata (Sow. sp.),
- Exogyra Texana (Roem.),
- Gryphoea Pitcheri (Mort.),
- Homomya alta (Roem.),
- Cardium multistriatum (Shum.),
- Holectypus planatus? (Roem.),
- and Toxaster Texanus (Roem.)
After leaving the Pecos crossing we wound our way amid rough hills and cliffs of the same geological constitution as those just described. Everywhere we found a barren soil, composed almost entirely of pulverized limestone.
Distance, 5½ miles.
May 13.-During the entire day we traveled through the valley of the Rio Pecos. For the first six miles the rocks do not differ in general appearance from those observed yesterday. Beyond this the hills assume a more regular outline and the cliffs are less rugged in their aspect, The former are generally smooth, of a conical form with truncated apices. At first they are closely aggregated, but as we progress they become widely separated by smooth and gently undulating prairie. Their height is from five to eight hundred feet, and they present every indication of having once formed a portion of the elevated table land, now several miles distant, and from which they have been separated by denudation. The different strata composing them are found to agree in every particular with those composing the table land. Near the summits of the highest of them the strata are very prolific in well preserved organic remains. The following are the