METALLIC VEINS. 27 
When the mountain is illuminated by the rising or setting sun this variety of color produces 
a novel and pleasing effect, redeeming, in some degree, the scene from the aspect of sterility 
and desolation which it would otherwise bear. 
MONUMENT MOUNTAINS AND CANON. 
For several miles above the Riverside mountain, the Colorado is bordered by the bluffs formed 
by the erosion of the desert plain. They are composed of conglomerate, sand, and clay, but 
slightly consolidated and entirely undisturbed. In some places the upper stratum, forming the 
desert surface, is filled with nodular concretions of calcareous tufa. At Beaver island we reach 
the foot-hills of the Monument mountains. The immediate banks of the river are composed of 
strata of a peculiar tufaceous conglomerate, apparently formed of volcanic ashes stratified by 
the action of water, above which are layers of white infusorial earth and beds of gravel and 
sand. Just above the head of Beaver island these strata are seen, much disturbed and meta- 
morphosed by masses of trap that have been thrown up into low rounded hills. 
Corner Rock is a large mass of metamorphosed conglomerate, a portion of the series which I 
have just described, against which the river impinges, and by which it is deflected from its 
ecurse. The conglomerate is overlaid by a thick bed of dark blue basaltic trap, which has 
here been the agent of metamorphosis. On the trap lies a bed of Quaternary gravel. 
Tbe series of strata exposed in this vicinity, including the conglomerate and the chalk-like 
infusorial rocks, I have supposed to be older than the beds of gravel and sand which border the 
river at so many points below, and to represent the Tertiary epoch. I shall have occasion 
frequently to allude to the recurrence of similar strata, in describing the geology of the banks 
of the Colorado between this point and the Rio Virgen. 
Soon after passing Corner Rock we entered Monument cafion, which is cut through the 
Monument mneieniains by the Colorado, its northern entrance being at the mouth of Bill 
Williams’s Fork. "Bh oughout the whole of its course this cafion abounds in wild and _ pictur- 
esque scenery, the. effect of the varied outline of its walls being heightened by the vivid and 
strongly contrasted colors which they exhibit. 
The great mass of Monument mountains is granitic, a rather coarse, massive, felspathic 
granite, in which the crystals of felspar are pink and the hornblende green. This granite is 
traversed in every direction by veins of different kinds. The largest and most conspicuous are 
quartzite and epidote, in which I detected no metallic substances. Other are composed of 
limonite and specular iron ore, of which great quantities are visible in the cliffs bordering the 
river. The veinstone associated with the iron is usually crystallized carbonate of lime. 
Another class of veins contains a greater or less quantity of copper, frequently combined with 
iron and manganese. Argentiferous galena was also found, but in small quantities. 
On either side of the granitic axis of the chain are thick beds of highly metamorphosed 
conglomerate and sandstone, which, according to the amount of iron contained, are deep blood 
red, pink, drab, or white. These beds of conglomerate compose the red and precipitous walls 
which form the southern entrance to the cafon, as also the lower portions of the tabular trap 
hills at the northern entrance on the east side. Overlying the conglomerates and sandstones, 
on the same side of the river, are thick masses of stratified trap, which form high and table- 
topped summits. Near the southern entrance the conglomerates are mingled with masses of 
blue, green, purple, white, and red trap, trachyte, and tufa, which furnish the most striking 
elements in the particolored pictures formed by the scenery of the cafion. Associated with the 
granite in many localities are exposed masses of highly crystalline pinkish, white, or cream- 
colored limestone. If this rock was at any time fossiliferous, its organisms have entirely 
disappeared in its metamorphoses. It, however, closely resembles the crystalline limestones of 
Riverside mountain and that which occurs at various points in the Sierra Nevada of California. 
A limestone, in some localities highly metamorphosed and resembling this, has been found in 
