STRUCTURE OF VALLEY AT FORT DEFIANCE. 93 
undermining the more resistant portion of the eastern cliff. This process is indicated by the 
present outline of the valley, its western slope being formed by the dipping surface of the 
saliferous sandstones, its eastern by the broken and abrupt edge of the indurated variegated 
marls and cretaceous sandstones. 
The drainage of the western slope has formed tributary valleys of considerable depth, much 
deeper, indeed, geologically, than the great trough into which they lead. These excavations 
lay open the Saliferous sandstone series to its base, and afford us the information of the struc- 
ture of the western side of the valley incorporated in the preceding section. 
The most important of these secondary channels—rather a cafion than a valley—known™to 
the occupants of the fort as ‘‘ Cafioncita Bonita,’’ is the worthy object of their admiration. 
From its more modest dimensions it has received the diminutive appellation it bears, but in 
picturesque beauty it is scarcely inferior to its grander namesake, the Cafion Bonito. 
Fig. 26.—srcCTION OF THE VALLEY AT FORT DEFIANCE. 
» 
artegaled marts. 
\Orelaccous rocks. 
Cretacecus rocks. 
WY Fa reegaled muarls 
\ i 
/ 
K 4 
U iri 
[/ 
AL 
‘ i, rt Detiance 
@ Sandstones and shales. 
6 Pink and white soft calc. sandstones. 
¢ Soft variegated marls, with fossil wood. 
f Red or whitish compact sandstone 
g Carboniferous limestone. 
x Trap. 
Between four and five hundred feet of the saliferous sandstones are exposed in Cafioncita 
Bonita, and in that over which is thrown the beautiful arch of the natural bridge. Asa whole, 
the sandstones of this group are lighter in color, more massive and compact, than on the Little 
Colorado. The conglomerate, however, presents precisely the same appearance here as there, 
specimens from the two localities being undistinguishable. 
Garnets and beryls of unusually fine quality are found in considerable abundance in the 
alluvial soil about Fort Defiance, and in the other portions of the Navajo country. As the 
region has never been swept by any general drift current, and the mountains of crystalline 
rocks are so remote, I have thought it probable that they were derived from the decomposi- 
tion of the conglomerates. I have never been able to discover any of them in this rock where 
Ihave examined it, but the gravel in which they occur is composed, almost exclusively, of 
