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For 8 or 10 miles below the mouth of the Little Colorado, the river is in the variegated quartzites, and a wonderful fretwork of forms and colors, peculiar to this rock, stretches back for miles to a labyrinth of the red wall cliff; then below, the black gneiss is entered and soon has reached an altitude of 800 feet and sometimes more than 1,000 feet; and upon this black gneiss all the other structures in their wonderful colors are lifted.
So these quartzites are aslant, and though of great geologic thickness, they make but 800 feet of the wall. Your books may have many-colored bindings and differ greatly in their contents; so these quartzites vary greatly from place to place along the wall, and in many places they entirely disappear. Let us call this formation the variegated quartzite.
In the central region the gneiss is covered by transition or sub-metamorphic rocks, consisting of a strong band of quartzites overlying a mass of earthy schists.
Down by the river the walls are composed of black gneiss, slates, and schists, all greatly implicated and traversed by dikes of granite. Let this formation be called the black gneiss. It is usually about 800 feet in thickness. Then over the black gneiss are found 800 feet of quartzites, usually in very thin beds of many colors, but exceedingly hard, and ringing under the hammer like phonolite.
Whilst the country to the north-east of the lakes is mostly composed of rocks, of great age, geologically, such as schists, quartzites, and old dolerytic rocks, with newer but still ancient trachytes, that to the south-west of them is formed principally of recent volcanic tufas and lavas, the irruption of which has not yet ceased.
The rocks chiefly are gneisses, granites, metamorphosed marbles, quartzites, and slates, all of them far too old to bear fossils or coal. "Git up, pup! you've scrouged right in hyur in front of the fire. You Dred! what makes you so blamed contentious?"
Even if we had not discovered the Eozoon, we might fairly have inferred from analogy that as the quartzites were once beds of sand, and the gneiss and mica-schist derived from shales and argillaceous sandstones, so the calcareous masses, from 400 to 1000 feet and more in thickness, were originally of organic origin.
More of the material is commonly rearranged by solution and redeposition, so that limestone may be converted into crystalline marble, granular sandstones into firm masses, known as quartzites, and clays into the harder form of slate.
Thus where a region is underlain by sedimentary rocks, as is the drift-covered area from the Hudson River to the Missouri, the drift contains not only fragments of limestone, sandstone, and shale of local derivation, but also pebbles of many igneous and metamorphic rocks, such as granites, gneisses, schists, dike rocks, quartzites, and the quartz of mineral veins, whose nearest source is the Archean area of Canada and the states of our northern border.
The geologists were interested, and we others learnt something of olivines, green in crystal form or oxidized to bright red, granites or granulites or quartzites, hornblende and feldspars, ferrous and ferric oxides of lava acid, basic, plutonic, igneous, eruptive schists, basalts &c. All such things I must get clearer in my mind. Tuesday afternoon a cold S.E. wind commenced and blew all night.
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