THE ALGONKIAN ERA
[Illustration: TILTED ROCKS OF THE SECOND ERA. GRAND CANYON]
Rocks formed during the second great era of the earth’s history are
distinctive in several respects. They are not highly altered or
completely changed in form and structure as are those of the oldest era,
but are largely free from such changes and, for the most part, similar
to rocks which are seen in the process of formation today. Furthermore,
they are known to contain definite traces of plant life, though no
certain forms of animal life have yet been found in them. They represent
a period probably as great as all of subsequent time.
ALGONKIAN ROCKS IN GRAND CANYON
Along Bright Angel Canyon and in several other places in the Grand
Canyon, rocks of Algonkian age, representing accumulations of sediments
several thousand feet in thickness, are found. Below and to the north of
Desert View (southeast of Cape Royal on the North Rim) they form the
open floor of the Canyon. Everywhere the most conspicuous layer of this
series is a mud rock of brilliant vermilion color. However, the rocks
also include a conglomerate or pebble layer, a dark limestone formed
principally by plants, and a purple quartzite made by the consolidation
of the grains of a sandstone.
FORMATION OF MOUNTAINS
(THE ALGONKIAN ERA)
The Algonkian rocks of the Grand Canyon region were bent and broken into
mountains at an early date. In many places sloping layers showing the
steep angle at which they were tilted are easily visible, even from the
Canyon rim. Folded areas and strata which have been shattered are also
conspicuous features here and there. The mountains which they formed,
however, are now missing for they were worn away in large measure by
slow erosion. Today only remnants—small hills on a general level
surface—remain in the lower parts of Grand Canyon to tell the story.
EARLY CLIMATES
(THE ALGONKIAN ERA)
The rocks of Algonkian age are roughly estimated to be at least six or
seven hundred million years old, yet from all indications they were
formed under conditions of climate not unlike those of far later periods
of history. In several parts of the world traces of great ice
sheets—glaciers which scratched and eroded the surface—are found
preserved in Algonkian rocks. In other places, including the Grand
Canyon, ancient flows of lava are found where they gushed out upon the
surface of an old land mass. Among the rocks below Desert View (Navajo)
Point and bordering on the Colorado River may readily be seen several
black cliffs formed by the volcanic activity of this early age.
The brilliant red shales of Algonkian age found in the lower parts of
the Grand Canyon were formed as muds, accumulated probably by large
rivers. In these muds are found preserved great quantities of ripple
marks, indications of changing currents, also the moulds of salt
crystals, and large shrinkage cracks resulting from a very hot sun. In
brief, these criteria point toward a hot and probably arid climate in
this region during that chapter of history.
OLDEST KNOWN LIFE
(THE ALGONKIAN ERA)
The oldest forms of life represented in rocks of Grand Canyon are found
in strata of the Second, or Algonkian, Era. Certain layers of limestone
showing peculiar structural patterns on their surfaces are interpreted
as being the reefs built up through the activities of primitive
one-celled plants known as algae. Similar structures are being formed
today by plants of this type. Near Harper’s Ferry, West Virginia, for
example, algae are building up limestone layers almost identical to the
fossil ones found in the Algonkian rocks of Grand Canyon. In this
connection, it is interesting to note that because of this similarity of
the present to the past, the reality of the ancient plant structures was
recognized a few years ago. They were discovered at a place in the Grand
Canyon just west of the mouth of Bright Angel Creek.
[Illustration: Rocks of the Third Era in the Grand Canyon]
Rocks of the Fourth Era (Red Butte)
Rim of Grand Canyon
a~ Sandy limestone formed beneath the sea. In it are found corals,
sponges, sharks’ teeth and many sea shells.
Kaibab Formation 300 ft. Permian Age
b~ Red sandstone and gray limestone. Formed at bottom of a shallow
sea.
Toroweap Formation 250 ft. Permian Age
c~ Wind-blown sand which was piled in dunes. Contains the tracks of
many kinds of primitive reptiles or amphibians.
Coconino Sandstone 300 ft. Permian Age
d~ River mud in which are preserved many impressions of ferns and
cone-bearing plants, insect wings, raindrop pits and tracks of
salamander-like animals.
Hermit Shale 300 ft. Permian Age
e~ Ancient flood-plain deposits of sand and mud containing impressions
of fern-like plants and tracks of land animals.
Supai Formation 800 ft. Permian Age
f~ Sea deposits containing remains of shells, fish, sea-lillies and
related forms of life.
Redwall Limestone 550 ft. Mississippian Age
g~ Accumulations of sandy lime in which are preserved the remains of
some of the earliest fish.
Temple Butte Limestone Devonian Age
h~ Sand, muds, and limes representing ancient beach which was
gradually covered with water until finally the sediments were
at a considerable depth beneath the sea. The earliest definite
traces of animal life in the canyon found here.
Tonto Rocks Cambrian Age
_i and j rocks of the First and Second Era_