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Updated: June 8, 2025
The grains of sandstone are held together by some cement. This may be calcareous, consisting of soluble carbonate of lime. In brown sandstones the cement is commonly ferruginous, hydrated iron oxide, or iron rust, forming the bond, somewhat as in the case of iron nails which have rusted together.
These lavas did not, however, come to the surface, but as they rose they lifted the sandstones, shales, and limestones, to a thickness of 2,000 or 3,000 feet or more, into great domes. Then the molten lavas cooled in great lenses of mountain magnitude, with the sedimentary rocks domed above them.
Below the plateau, slight slopes lead the eye to the last of the stratified rocks, the Tonto sandstones of the Cambrian period. These are readily distinguished, mainly by their deep buff color and the fact that generally they are found resting on the archaean or unstratified rocks, locally though incorrectly termed the granite, which makes the Inner Gorge through which the river runs.
The massive strata are the horizontal elements in the entablature, but the intervening shales are carved with a beautiful fretwork of vertical forms, the sculpture of the rills. The massive sandstones are white, gray, blue, and purple, but the shales are a brilliant red; thus variously colored bands of massive rock are separated by bands of vertically carved shales of a brilliant hue.
This, together with the fact that sandstones are not formed far out at sea, justify the safe conclusion that the land could not have been far off.
After a time this layer of vegetable matter was slowly and gently let down beneath the waters of the sea so slowly that the water flowing over it did not, as a rule, disturb the loose, pasty mass; and then, by the method I have described to you, shales and sandstones were deposited on the top of this mass of dead vegetable matter.
The course of the Amazon, which is first directed north, then east, changes near Puyaya, three leagues north-east of Tomependa. Throughout the whole distance between Tambillo and San Borja, the waters force a way, more or less narrow, across the sandstones of the Cordillera of Chachapoyas.
Perhaps now and then the basins became long, brackish estuaries, whose low shores were swept by the incoming tide and were in turn left bare at its retreat to receive the rain prints of passing showers and the tracks of the troops of reptiles which inhabited these valleys. The Triassic rocks are mainly red sandstones, often feldspathic, or arkose, with some conglomerates and shales.
Yellow pines, nut pines, firs, and cedars stand in extensive forests on the Uinta Mountains, and, clinging to the rocks and growing in the crevices, come down the walls to the water's edge from Flaming Gorge to Echo Park. The red sandstones are lichened over; delicate mosses grow in the moist places, and ferns festoon the walls. The Yampa enters the Green from the east.
In many places distinct proof is seen that the enveloping strata took years to accumulate, for some of the sandstones surrounding erect sigillarian trunks support at different levels roots and stems of Calamites; the Calamites having begun to grow after the older Sigillariae had been partially buried.
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