TO JUNCTION OF GRAND AM) GSEBN EIVBBS. 71 



in some places 150 feet thick. Above the marls are the yellow sandstones — the base 

 of the Cretaceous — which floor tlie plateau on either side. Pursuing a northerly 

 direction, we gradually rose through the Trias, and at Navajo Springs reached the base 

 of the ( Yetaceous sandstones. ( Jontinuing our ascent, two or three miles farther on we 

 reached the base of the canon, and emerged upon the plateau of which I have before 

 spoken. This plateau extends northward to the Yada del Chama, where it begins to 

 be broken by the foot-hills of the mountains. Westward it reaches to and beyond 

 the source of the Chama, and is broken through and locally disturbed by the upheaval 

 of the Gallinas Mountain, which seems to be situated on the Nacimiento axis. Over 

 this plateau the Lower Cretaceous sandstones form the general substratum, but here 

 and then; are rounded knolls, composed of the dark shales and blue shaly limestones, 

 the lower part of the middle division of the Cretaceous formation, here, as at a thou- 

 sand other points on our route, characterized by the presence of GrypJiea Pitcheri, Ino- 

 ceramus problematictoSj Ostra congesta, (Sec. The more level portions of the plateau are 

 covered with sage bushes, with here and there more moist and fertile spots, sustaining 

 grasses and annual plants, conspicuous among which is the wild suntlower (IIcI'hui- 

 fl/ns). The knolls are usually covered with proves of pifion. As a whole, this pla- 

 teau country has little agricultural value, although there are portions of it which will 

 afford good grazing for stock. 



Between the Cebolla and Nutria, the Middle Cretaceous rocks occupy a consider- 

 able area, and attain a thickness of perhaps a hundred feet. They present precisely 

 the same lithological characters and fossils as do their equivalents on the banks of the 

 Canadian and Ocate*, east of the Rocky Mountains, viz., thin layers of hard dark- 

 blue or ferruginous limestone alternating- with layers of bitumino-calcareous shales. 



At the Yada del Chama we again encamped on the banks of this stream in a very 

 beautiful region, one of considerable fertility and of great geological interest. On 

 the east side of the river are high and broken hills — the foot-hills of the mountains — 

 covered with forests of splendid pine timber. These hills are mainly composed of the 

 Lower Cretaceous sandstones, having a thickness of nearly 300 feet. Here, as farther 

 west, they contain beds of lignite, and the impressions of dicotyledonous leaves. They 

 are considerably broken up, but have a general and rapid dip toward the southwest. 

 On the opposite side of the valley is a mesa, with bold, nearly perpendicular faces 

 over 1,000 feet high, composed of the Middle and Upper Cretaceous rocks lying nearly 

 horizontal. Between these elevated banks lies the excavated valley of the river, with 

 its narrow but fertile bottom-lands, its winding stream of pure cold water, its groves 

 of cottonwood, and its grassy meadows spangled with tlowers. The structure of the 

 valley will be more readily comprehended from the accompanying section than from 

 any detailed description I could give of it. 



Transverse section of the valley of the Chama ai lite Vada. 



Foot. 



1. Yellowish brown sandstone (Lower Cretaceous) 125 



2. Brown and black shales, often dark olive, with beds of lignite . 50 



3. Sandstone similar to No. 1 70 



