第38章 CHAPTER XIII(1)

How The Canyon Was Formed*

* This chapter, while in manuscript, was read by Dr. Charles D. Walcott, Secretary of the Smithsonian Institution and formerly Director of the United States Geological Survey, and also by Professor Matthis, of the Survey. It may therefore be accepted as a fairly accurate and authoritative presentation of the geological conditions existent at the Canyon, with their explanations, as accepted by the leading scientists of to-day.

The beginning of land. In the long ago centuries, when the world was "without form and void," waters covered the face of the earth, and darkness brooded over the waters. As the earth's crust began to shrink under the water, in the process of cooling, the first masses to crumple up, to wrinkle, were the first to arise above the surface of the vast, primeval, shoreless ocean. They appeared as tiny islands, pinnacles, or ridges thrust up, exactly as we see them sometimes on the coast,--hidden at high tide;appearing again at low tide.

The Laurentian Hills. Nature had plenty of time before her, so she did not hurry her work, and it took long centuries before there was any large amount of land thrust up out of the bosom of the sea. The scientists are able to tell us, with some definiteness, which came forth first. They say that on the continent of America the earliest born land was a mass of granitic rock in Canada,--the Laurentian Hills. The next to peer above the surface and feel the warmth of the sun were peaks and ridges that made islands of themselves, in what are now known as the Rocky Mountains and the Appalachians. Now, at last, the great waves of the sea and the resistless storms had something to play with, and they pounced down upon the land as with tooth and claw. They rubbed and pounded, raged and smashed for a thousand years, and then another thousand, and still another, while Mother Earth uneasily thrust forth her rocky children out of the ocean into the light of day. Surprised at such treatment by the storms and seas, the newly born earth masses began to crumble and "weather." The detached fragments slipped back, or were washed back, into the deeper or shallower parts of the ocean, and were there tossed back and forth, pounded and ground into sand and silt, into pebbles and boulders, while more land was slowly being thrust out for the angry sea to work upon. Layer by layer, the ground-up masses were deposited in the inner ocean bed, parts of which were now practically shut off from the vast ocean beyond. How many centuries of centuries this process continued geologists do not tell us. Time is so vast, so long, that they cannot divide those early days into weeks, months and years, as we now do.

The Continent is born. After many millions of tons had been thus ground up and tossed about and mingled with the waters of the seas, the earth, in a fit of fiery anger, turned and baked them, with intense heat, out of all semblance to their former appearance. These baked masses, in the course of time, were thrust up out of the seas, mashed and macerated once more, again deposited as sand, silt, pebbles and boulders, and again burned. These processes followed each other, how many times we do not know, the earth all the while keeping up her steady uplift of the children of her bosom out of the great sea. Higher and higher came the land. Further and further receded the sea, until, in due course, the sun shone upon a vast area of land that was the rude skeleton of what is now the continent of North America.

It would have taken a keen eye, however, to have imagined from that which we see to-day what was there. The Gulf of California reached far up, even into Nevada, and covered what are now the Mohave and Colorado Deserts;there was no California Coast Range; the Gulf of Mexico was vastly larger than it is to-day, covering all Florida, and reaching up the Mississippi Valley half-way to the Great Lakes.

The First Strata. It was just preceding the last uplift of this epoch that the era of deposition of rock debris was so prolonged that twelve thousand feet of strata were washed into the bed of the sea, in the region now known as the Grand Canyon Country. It was at the time when life was beginning to dawn, for in the remnants of the strata are found fossils of the earliest known life. These strata, therefore, are of immense interest to the geologist, as they are the first known rocks containing life to emerge from the primeval sea. Within the last few years, they have been called the Algonkian Series, and later I shall speak of them more freely.

Prior to the deposition of these Algonkian strata, the Laurentian rocks (the granite) upon which they rest were subject to a long period of "planation,"--as the grinding down and leveling of rock surfaces is termed.

After this planation was complete, a subsidence occurred; the whole area became the bed of an inland sea, and upon the planed-down granite, the debris that formed the Algonkian strata was washed.

While they were being deposited, the whole region was the scene of several seismic and volcanic disturbances, for great dykes and "chimneys" of lava are found, showing clearly that, by some means or other, the strata were broken and shattered, cracked and seamed, and that through these cracks the molten lava oozed--forced up from the interior of the earth. It spread out over the Algonkian rocks in small sheets or blankets, which here and there are still to be found to-day.

Tilting of the Algonkian Strata. Slowly this twelve thousand feet of strata emerged into the sunlight. In the uplifting processes, the surface of the earth, where they were, became tilted, and these strata therefore "dipped"or "tilted" away from the perpendicular. As they emerged, weathering and erosion began. It is most probable that this process of degradation began and continued while the topmost strata were at or near sea level, so that it was a simultaneous process with the uplift.