180 
THE GKAND OASON DISTEICT. 
The age of this series is probably Silurian. Devonian beds may also 
be found in its upper part, but all that we can say about their age now is 
that they are pre-Carboniferous. Lithologically, they appear at a distance 
veiy much like the rainbow beds at the base of the Trias and summit of the 
Permian in the Valley of the Virgen. The bedding is very uniform and 
regular. The colors are chocolate, purple, lavender, and magenta, of many 
tones and shades. If it were not for this powerful coloring, which discloses 
every band and layer with emphasis, and each with a habit peculiar to itself, 
we could not venture to assert so much about them as we have done. For 
we have been reading geology five to ten miles away from our rocks. But 
what are miles in this Brobdingnagian country! These things seem to lie 
at our very feet. 
Just where the comparatively narrow gorge of the Marble Canon ex- 
pands well out into the much ampler width of the Grand Canon, we per- 
ceive among the higher beds of this ancient series some layers which we do 
not hesitate to pronounce volcanic rocks — basalts or diabases. They are 
coal black, and contrast finely with the rich colors all around them. They 
are interbedded with the upper Siluriaii (?) strata, but whether they are 
intrusive sheets or contemporaneous coulees, outpoured while the rocks were 
accumulating, we cannot say. The very dykes through which the lava 
came up are visible. Powell saw them on his boat journey down the river, 
but did not have an opportunity to investigate the many interesting questions 
which they suggest. 
Throughout the remainder of the canon, although the pre-Carbonifer- 
ous rocks are laid open for more than half the distance, there is no such 
exposure of early Paleozoic strata. Wherever the lower quartzites are cut 
through they are usually found resting upon the schists. In several places, 
however, remnants which correspond to the base of this Silurian series 
are disclosed betu'een the quartzites and the schists, but the mass seldom 
exceeds 200 feet, and, perhaps, never reaches a thickness of 400 feet. A 
few Primordial trilobites have been found in these remnants. The meaninff 
of this great unconformity obviously is that after a vast body of early Pale- 
ozoic strata had been laid down they were distorted by differential vertical 
movements, were flexed and faulted, and were elevated above the sea. 
