MESOZOIC EOEMATIONS. 
5 
thin beds of a light-brown color, containing numerous broken fish-bones 
and Ostrea congesta, &c.; the appearance resembling closely fish-bearing 
shales found by Professor Mudge near Stockton, Kansas. From Tierra 
Amarilla, the route of my party laid southwestward. After crossing the 
river, and the bluffs which bound its immediate valley five miles beyond it, 
the sandstone,of Cretaceous No. 1 rises from beneath the Cretaceous No. 2 
with a southeast dip. In some places, it rises abruptly like the wall of a 
fault, forming vertical bluffs of greater or less elevation, facing the east. 
This axis of elevation is at this point narrow, and the sandstone is soon 
found to dip to the southwest, west, and northwest. The route continued 
for forty miles along the western base of this line of elevation, which in¬ 
creases in importance as we proceed southward. At first, the Cretaceous 
No. 1 sandstone forms extensive barren, slopes of 15° to 20°, constituting 
the northwest flank of the gradually-rising Gallinas Mountains; but farther 
south, where the mountain reaches its greatest elevation, it is steeper and 
more broken. 
The structure of the region west of the Sierra Madre from this point 
as far as my investigation extended (fifty miles) is a beautiful repetition of 
that observed and described on the east slope of the Rocky Mountains, so 
far as the Mesozoic strata are concerned. The mountain-axis itself exhibits 
great variations in its surface-formation and elevation; but the position of 
the beds on its flanks is remarkably uniform,- These form a series of hog¬ 
backs, formed by Cretaceous Nos. 1 and 3, and occasionally by harder 
beds of Nos. 2 and 4, which are separated by parallel valleys, which are 
often grassed and timbered, and rarely occupied by sage-brush. The most 
important of these is that lying between Nos. 1 and 3. The upper portion 
of the Chama flows through a similar valley on the eastern side of the 
Gallinas axis, and is turned aside by that line of elevation, and then cuts 
through the beds of No. 1 and the overlying formations, and finally through 
the axis of elevation farther eastward, reaching the Trias before entering 
the Santa Fe marls. On the western side of the axis of the Gallinas, the 
valley of Cretaceous No. 2 exhibits two points of elevation. The most 
northern is near the Rio Chama; the southern and highest, at the head of 
the Rio Puerco. From the latter, the drainage is carried through the Gal- 
