THE LOUP FORK BEDS. 
23 
river, which form part of the Santa Fd Tertiary marls, as proven by the 
occurrence of the bones of Mastodon and Aceratlierium jemezanum, Cope, 
near Santa Cruz. 
The orange beds are doubtless older, and were afterward seen on the 
Chama River; but I was unable to determine their age or their precise 
relation to the overlying sands and marls. They are covered near the 
mountains by a mass of basalt, which forms the floor of a higher mesa, from 
which rise the basaltic cones of the Jemez Mountains. Some of their peaks 
were doubtless sources of discharge of lava at a former period. I did not 
observe that the orange beds were tilted, or rested other than nearly hori¬ 
zontally against them. 
In the ascent of the Rio Chama, we pass over the Santa Fti marls 
exclusively until reaching the town of Abiquiu. Here are bluffs of 700 feet 
elevation, of a soft sandstone, having the same character and dip (10° to 
15° northwest) as those above described as at the eastern base of the Jemez 
Mountains. In a bay on the western side of one of these bluffs is a patch 
of picturesque bad-lands of the Santa F^ marls. Five miles above Abiquiu, 
the brilliantly-colored yellow and red beds, which form such an important 
feature in the geology of Western New Mexico, appear in high bluffs on the 
north side of the river. They are several hundred feet in thickness, but, 
near the Rio Chama, descend so as to permit of a view of their relations to 
the superincumbent beds. The brightly-colored beds are cut by a ravine 
to a depth of about one hundred and fifty feet. The upper portion is yellow, 
and they dip 25° southwest. Tliey are overlaid by a shale of fifteen feet 
in thickness, whose laminae are frequently contorted. The lower part of 
the bed is finely laminated, and the upper portion consolidated into a very 
hard rock. Above it is a bed of twenty feet, of a very coarse conglomerate, 
whose cement is arenaceous. 
These details are entered into for the purpose of exhibiting the uncon- 
formability between the late Tertiary beds of the Rio Grande Valley and 
the formations constituting its western shores. The beds just described 
are believed to correspond with those called Jurassic in the section taken at 
Colorado Springs, and quoted earlier in this chapter. Red beds, sup¬ 
posed to correspond with the Trias of the same section, were observed by 
