TO JUNCTION OF GRAND AND GREEN RIVERS. 33 



Wherever I have observed them these different divisions are marked by obvious and 

 distinctive Hthological characters, and the fossils contained by each group are usually 

 recognizable at a glance. Those of the Lower sandstone group being generally angi- 

 ospermous leaves; those of the Middle group, marine shells and the remains of fishes; 

 those of the Upper division, as far as yet observed, being leaves and trunks of trees 

 different from those found below. It is true, that in Southeastern New Mexico and 

 Texas there is veiy little sandy matter in any of the Cretaceous rocks, while in the 

 Rocky Mountains the upper and lower arenaceous divisions are greatly developed, and 

 the limestones have nearly disappeared from the middle division. This latter group is, 

 however, distinctly marked even there; consisting of calcareous shales, with thin bands 

 of limestone and beds of lignite, interstratified with layers, of greater or less thickness, 

 of fine-grained sandstones, usually containing considerable lime. 



On the banks of the Canadian, from 800 to 1,000 feet of the Middle Cretaceous 

 strata all exposed. 



The section from the summit of the hills at the "Breaks of Red River," down to 

 the bed of the stream, is as follows: 



1. Rolled gravel, composed of fragments of porphyry, trap, Paleozoic limestone, 

 &c., drift from the Rocky Mountains. 



"2. Light-blue compact limestone, on exposure cracking into flattish chips or 

 "spalls," containing Inoccmmus problemati&us, Gryphcea Pitcheri, &c. 



3. Ferruginous, laminated, sandy limestone, with rounded concretions, one to five 

 feet in diameter, of compact blue limestone, much cracked, and fissures filled with 

 crystallized carbonate of lime. This rock is a great store-house of fossils, of which, 

 perhaps, the most abundant is a remarkably neat little Ostrea, hitherto undescribed, 

 which I have called Ostrea clcgantula ; one of the most common and widely distributed 

 Middle Cretaceous fossils of New Mexico. With this are Inoceramus frayilis, H. & M., 

 /. Crispiif, Ammonites percarinatus, Shark's teeth (Lamna and Oxyrhma), &c. The 

 surfaces of the layers of this stratum are covered with small Ostreas (0. conyeata), and 

 fragments of Inoceramus, which resemble fish-scales; thickness 80 feet. 



4. Light-blue compact limestone in thin beds, weathering white, similar to No. 2; 

 about 30 feet exposed. From this point to the bed of the river, some 700 to 800 feet, 

 the cliffs are composed of blue compact limestone in thin beds, alternating with dark- 

 blue and brownish bituminous calcareous shales, which underlie the preceding mem- 

 bers of the section, and rest upon the Lower Cretaceous sandstones In every part of 

 these lower limestones Inoccrannis problematicus is exceedingly abundant. They also 

 contain large numbers of (iriiplKca I'l/cl/cri, of which remarkably large and fine speci- 

 mens were collected a- short distance east of the crossing. 



All the foregoing calcareous beds rest upon the sandstones of Lower Creta- 

 ceous age to which I have so frequently referred. These sandstones form the bed of 

 the Canadian at the crossing and the walls of the canon below, and here exhibit nearly 

 the same Hthological characters as at many localities where they are exposed farther 

 eastward. They seem to be somewhat disturbed and hardened, and it is possible that 

 a slight unconformability may be discovered between them and the overlying rocks- 

 This is a mere suspicion, however, which I could not verify or disprove in the time at 

 5 s F 



