Geology Reference
In-Depth Information
an orange from the bottom of the pile. And that's when it's dry. Saturated sand can hold
a slope only about half that steep—nowhere near a vertical wall. In contrast, wet clay is
cohesive enough to support short vertical cliffs. If the creationist view held water—that
the canyon's slopes formed when the sediment was still saturated—then the slopes today
would have shale cliffs and sandstone benches, the opposite of what's visible along the
trail.
How long does it take for the finest sediment to settle out? Even in a bucket of still water
it can take weeks for fine clay to drop to the bottom. The distinctive microrhythm of coarse
to fine, coarse to fine, coarse to fine in the walls of the canyon proves how the now rock-
solid sediment settled out from a series of flows. The hundreds of thousands, if not mil-
lions, of layers of silt could not have settled out and separated from the intervening layers
of sand during the passage of a single violent current because turbulence would have re-
suspended the fine sediment. Individual layers of clay, silt, and sand take a long time to
segregate out—and far longer to do so over and over again to build up a pile it takes hours
to hike up through.
Every step brought me closer to the canyon rim, and I passed into the soft, easily eroded
Hermit Shale, where the slope relaxes and piñon pines and juniper trees manage to hold
down a thin soil. Within the rust-colored shale below the soil, fossil ferns, conifers, and the
tracks of reptiles and amphibians revealed the former nature of the region. I had climbed
out of an ancient ocean and into the remains of a temperate coastal jungle.
Passing out of the Hermit Shale, I started up more switchbacks and crossed onto a
massive, strikingly white sandstone. Composed of pure quartz sand, the Coconino Sand-
stone exhibits cross-beds that define the faces of fossilized sand dunes rising diagonally
through cliffs along the trail. Invertebrate tracks and burrows are preserved in these fossil
dunes. One outcrop near the trail preserves reptilian footprints that displaced the sand,
sending it slumping back down the face of a dune. Such fine-scale features would have
been obliterated if they had formed underwater, the way waves running up a beach erase
footprints in the sand. These dunes were made by wind.
Continuing my trudge, I passed through the yellow-gray Toroweap Formation, evidence
that a sea submerged the desert sands of the underlying Coconino Sandstone. Then a final,
grueling climb up the nearly vertical white wall of Kaibab Limestone. Plodding past day
