Science in Christian Perspective



Cordelia Erdman
Instructor in Geology
Wheaton College

From: JASA, 2, (June1950): 13-17.

The Grand Canyon of the Colorado River has often been likened to a book whose pages reveal the story of many eons of earth history. The story is told not alone by the relationship of the rocks to one another and the relationship of the river to the overall structure, but in large measure by the remnants of life preserved in these rocks. Here on a vast scale and in an accessible form is a completely unprejudiced account of ancient life.

Since paleontology, the study of ancient life, is so frankly geared to evolutionary philosophy, it sometimes faces the accusation of tailoring facts to fit the philosophy. The present paper is neither intended to be such an accusation nor designed to be a defense of paleontological method; rather, it is merely an account of a succession of life forms as they actually occur in the Grand Canyon. This account will be proffered without aid of any supporting philosophy.

Some simple principles of geology will provide a background for this description:

The most common rocks at the earth's surface are those which are termed "sedimentary." Before becoming rock they are merely loose sediment which has been deposited in essentially horizontal layers by water or wind, in the sea or on land. Each layer of sediment, in fact each particle, is deposited in response to certain very precise chemical and physical conditions, and so long as those conditions prevail, either locally or over a large area, the resulting sedimentary deposits will be of one characteristic type and texture. Any change in the controlling conditions is manifested in a corresponding type of sedimentation which gives the ultimate rock its own differentiating character or lithology. Such changes may take place abruptly or gradually. Thus a relatively homogeneous layer of rock represents the persistence of relatively homogeneous environmental conditions during a short or long period of time* Vertical successions of such layers are the "strata" of geology,

Marine deposition of sediment, the most common type, cannot take place indefinitely upward. 2ach site of sedimentation has its own governing "base level" an horizon above which there can be only erosion and below which there can be only deposition. Thus the presence of a thick series of rock layers shows that the region must have been sinking in order to make continuous deposition possible.

The sea may gradually withdraw from an area and thereby establish a new and lower base level. The even surface of the newly exposed layer will then be subject to attack from forces of erosion, and if this region once more sinks beneath the sea and sedimentation is renewed, there will be a highly irregular contact between the old and new layers. Pebbles and boulders of the old lower stratum may be incorporated in the base of the now one, thus clearly showing the relative ages. The record of all these events will be preserved in the rock which is formed by a process of gradual hardening due to pressure from overlying material and the action of cementing agents. Thus in a vertical senuence of undisturbed horizontal sedimentary strata, each stratum is younger than that below and older than that above*

Although sedimentary rocks are for the most part laid down in horizontal layers, they may later slowly become folded and bent by earth processes. Folded layers may become beveled by erosion and then have horizontal layers of sediment deposited on top when the sea again covers the region. The resulting contact of nonparallel layers is called an "angular unconformity." Obviously, those layers which truncate are younger than those rocks which are truncated.


This diagrammatic profile or cross section of the Grand Canyon shows the relationship of the strata on the north side of the Colorado River. All of the horizontal layers are sedimentary* Note that each has a symbol representing its own lithology (rock character). Also observe that the rock composing the canyon rim must be much younger than, for example, the rock of the Tonto Platform, since it is at the top of a series of undisturbed horizontal sedimentary strata. (Radioactive age determination indicates the passage of more than 250 million years during the formation of these layers).

Below the rock of the Tonto Group is another series of sedimentary layers, sloping markedly to the north and the east. This contact is an angular unconformity* Therefore we know that the Tonto Group is younger than these sloping layers which it truncates.

This second group rests in turn angularly upon, and is therefore younger than, a flat erosion surface which was formed on some badly deformed rocks. These were' once sedimentary but were squeezed and distorted in such fashion that they lost their original character and some layers were forced nearly vertical. Since the flat surface of erosion must have been horizontal when the next layers were deposited upon it, but is nom, sloping parallel to the layers deposited upon it, a great disturbance must have simultaneously affected all of the rocks below the Tonto Group.


The block diagrams will explain these events and make clear the relative ages of the rocks in question. The bottommost layers which we shall call "Rocks of the First Era," were originally deposits of sandstone and mudstone. Great pressure from the northwest and southeast pushed the layers up into mountains probably comparable to the present day Alps* Heat and pressure caused the rocks to recrystallizes into a form known as schist, and intrusions of molten rock broke through from below* (Diagram 1).

Erosion wore down the mountains to a nearly level plain during what must have been a vast span of time (Diagram 2).

Over this surface the sea came, causing deposition of more mud and sand. (Diagram 3). We shall call these "Rooks of the Second Era." This time the region was uplifted with little folding involved and these Rocks of the Second Era were broken through together with rocks of the First Era, causing huge blocks to slide upon one another,, forming mountains, as is shown in Diagram 4.

These mountains in turn were worn down, probably even while they were being formed* (Diagram 5).

Once more the sea came in. The roots of the mountains of the second era were at first islands in this sea, and then as sinking continued they finally were buried beneath the sediment which now forms the lowest of the Rocks of the Third Era, (Diagram 6). Continued alternate sinking and rising of base level is responsible for the rest of the story.

SLIDE 1 again

It is not possible to give any other logical explanation of the relationship of the strata shown in this profiles The Rocks of the Third Era must be successively older from top to bottom, the Rocks of the Second Era must be older still, and the Rocks of the First Era oldest of allo The strata are clearly superimposed in chronological order. Subsequent gentle doming of the whole region has enabled the river and its tributaries to cut the mile-deep canyon, leaving all of this history plainly exposed to view.
in nature.


This photograph will show the clarity of the contacts as they actually appear


Farther back on the plateau into which the Canyon is now cut there are remnants of other layers which at one time covered the whole region. These are the Rocks of the First Era. Their relationship to the Third Era is clearly shown by the accompanying cross section. They are flat, generally undisturbed layers and are unquestionably younger than those of the Third Era upon which they rest conformably. On top of them, but exposed even farther back from the Canyon, are the rocks of the Fifth Era. Thus within an area of one day's journey strata from the First to the Fifth Eras may be seen resting upon one another in consecutive order.


Nearly all of these layers contain some fossils. Here is an almost unparalleled opportunity to investigate the actual order in which various types of plants and animals are found fossilized, at least in this area.

Mother because they were actually absent or because they were destroyed in the course of mountain building, no fossils are found in the rocks of the First Era. Thus the first actual life is represented by colonies of fossil algae, some of the simplest of all plant life, in the layers of the Second Era. The preservation of algae may seem incredible, but comparison of them with modern ones shows them to be so strikingly alike that there can be no doubt of their validity. Sponge spicules have also been tentatively reported from the same layers and if this becomes verified, it will be of interest that the first remnant of animal life belongs to a group of exceedingly simple organization. Sponges are considered to be the most "primitive" of the manycelled animals. In all of the layers from the rocks of the Second Era upward there are found certain tubes which are most readily interpreted as worm burrows and have been so accepted by most paleontologists.

The lowest layer belonging to the Third Era is called the Tapeats sandstone. In this sandstone are found algae in the form of sea weed, and marine animals belonging to two different divisions of the invertebrates (animals without backbones). one group comprised several species of scorpion-like creatures that are now extinct, and the other was composed of brachiopods, bivalved animals, mostly rather simple.

In the Bright Angel Shale, which lies upon the Tapeats sandstones different genera and species of the preceeding groups are present. In addition there are other seashells some doubtfully referred to the molluscs, others related to sea lillies, which are really animals, a primitive crustacean or crab-like animal, and a coral-like form of unknown affinity*

The next highest layer is the Mauv limestone and in it are Pound only different genera and species of the animals of the preceeding shale. The Huav underwent a period of sub-aerial erosion during which great river channels were out into it. 711hen sediment was again deposited over the region by the sea, sand and lime together with fish remains were swept into these old channels. Later erosion removed all of what is called the Temple Butte limestone except that which was in the river channels, and so it is here that vertebrate life is first recorded in this secuenceo The fish were cui+e unlike those we know in that they had a bony armour over the major portion of their body and scales only in the hinder portions.

The Redwall limestone, resting upon the Temple Butte and Muav, contains the shells of marine invertebrates. In addition . to many genera of braohiopods there are fragments of sea  lillies, some true colonial corals and a type of moss animal or bryozoan.

Lying above the Redwall limestone is a great thickness of alternating sandstone and shale, the Supai Formation, which represents a delta and river flood plain environment. Here are found corals, brachiopods and true molluscs, such as clams and cockles, but of even greater interest has been the discovery of the tracks of large four-footed creatures which seem to have beer- some kind of amphibian. Reptilian type tracks have also been found. The plant life of the time included ferns, the simplest of land plants,

The next youngest layer, the Hermit Shale, presents one of the most interesting array of fossils in the entire strata of the Canyon. it, too, is a land deposit, probably the flood plain of a great river in an arid region. Here are found footprints of salamander-like animals, wings of giant insects and 35 species of plants, including primitive conifers or evergreens.

Immediately above the Hermit Shale is the Coconino Sandstone, a deposit of wind blown dunes, The only traces of life in this rook are the tracks of insects and at least 27 species of amphibians.

Following deposition of the Coconino sands, there was a new invasion of the sea and in the
1,aibab formation which rims the Canyon there are the remains of corals, sponges, sea lillies and sea shells. Many of these genera also occur in the lower layers, but in some cases the species of duplicate genera show a greater degree of complexity in these upper layers. Shark's teeth are found in the Kaibab but not in any other of the marine deposits which otherwise have somewhat similar faunal associations.

In summary, the rocks of the Third Era show first simple plant life and primitive marine invertebrate animals only, then fish remains and some different marine invertebrates. Next are found ferns, then evergreens, and in conjunction with these are the tracks of amphibians and reptiles and the imprint of insects. Finally there are a host of marine invertebrates and some shark's teeth.


The lowermost layer of the Fourth Era is nearly lacking in fossils, but in the Shinarump and Chinle strata above it occur the famous petrified forests. The trees of these forests are largely conifers, but four or five other species are reported to be present. (Unfortunately, detailed information about the plant life of all these Bras was not accessible at the time of writing this paper). The jaw of a relative of the crocodiles has been found in one of the forests, showing that at least one large species of amphibian lived at that time. Fresh water clam shells have been found in association with fern impressions in this region. The seas supported a great variety of life including many types of molluscs, some snails, cruataceans moss animals, worms, sea lillies, corals, reptiles and fish.

It is in the overlying layers that the tracks and bones of dinosaurs are common. Dinosaurs were true reptiles, not amphibians, and the environment in which they were preserved for posterity as skeletons seems to have been that of river flood plains. Their known associates were other reptiles and some frog-like creatures. All of the reptiles reached quite astounding sizes before the end of the Fourth Era.

In rocks of the latter part of the Fourth Era mammal remains can be found and there is a great decline in the number of reptilian fossils. Intercalated coal beds indicate that there was luxuriant vegetation, and this is borne out by the presence of bits of fossil wood and foliage of deciduous trees.

Records of life we exceedingly sparse in the Fifth Era rooks., largely limited to fresh water clam shells which may be seen at Bryce Canyon. However, to the west of Grand Canyon at least one deposit of bones has been found which contained elephant tusks and camel and bison teeth, and to the southwest human artifacts have been discovered in association with such teeth. These deposits are localized and, because of lack of information concerning their relative age actually should not be included within the scope of the Present survey. Nevertheless, it is certain that they are of a later period of the Fifth Bra than that displayed at Bryce Canyon*

Thus in passing from the First to the Fifth Eras we have seen that simple plant life and possibly animal life of low organization occur in the Second Era; that some animals, namely the marine invertebrates, are found in one form or another from the beginning of the Third Era, and that starting in the middle of the Third Era, Vertebrate animals appeared successively as fish, amphibians, reptiles and mammals. Plant life is successively recorded in algae, ferns, conifers and deciduous trees.

Possible explanations of all this and the questions which it raises cannot be discussed here, The fact to be emphasized is simply that in the Grand Canyon and its environs the fossil picture is one which does show a sequence from what have been denoted "simple" forms to those which have boon denoted "complex" Whether this be a freak, of preservation, a more coincidence, or whether it holds deeper significance, the fact of its existence should not be overlooked.