magma sent upward by the mantle broke through the crust and crept over the land; repeatedly erosion cut it away and left new forms much different from their predecessors.
The time required! The slow passage of years! The constant alterations! Now part of an uplifted mountain, now sunk at the bottom of some sea, Centennial experienced wild fluctuations. Because of the erratic wanderings of the earth, it stood sometimes fairly close to the equator, with a baking sun overhead; at subsequent times it might be closer to the north pole, with ice in winter. It was swamp during one eon, a desert the next. Whenever it came to temporary rest, it should have been exhausted, a worn-out land, but always new energies surged up from below, generating new experiences.
Those lost two billion years lie upon the consciousness of man the way vague memories or ghosts survive in the recollections of childhood. When man did finally arrive on the scene, he would be the inheritor of those vanished years, and everything he did would be limited to some degree by what had happened to his earth in those forgotten years, for it was then that its quality was determined, its mineral content, the value of its soil and the salinity of its waters.
About three hundred and five million years ago occurred what can be called the first event which left an identifiable record at Centennial, and with it our story begins. Within the mantle, forces developed which produced a penetration of the earth’s crust. The basement broke into discrete blocks, some of which were pushed upward higher than their surroundings, to relieve the pressure from below.
The resulting mountains covered much of central Colorado, following fairly closely the outlines that the historical Rocky Mountains would later occupy, and at the conclusion of five or ten million years they constituted a major range.
It was not born in cataclysm. There was no dramatic opening of earth from which fully formed mountains emerged. Nor was there any excess of volcanism. Instead there was the slow, unceasing uplift of rock until the new mountains stood forth in considerable majesty. They were the Ancestral Rockies, and since they left behind them rocks which can be analyzed, we can construct for them a logical history.
They were not soaring peaks, like their successors, but they did rise from sea level and would have seemed higher above their pediment than today’s Rockies, which although they lift far into the sky, take their start from plains already high.
From the moment of their birth they participated in a startling series of events. No sooner had they pushed their crests above the flat surface of the land than small streams began to nibble at their flanks, eating away small fragments of rock and sand. High winds tore at their low summits, and freezing winters broke away protuberances. At intervals earthquakes toppled insecure rocks; at other times inland seas lashed at their feet, eroding them further.
As the mountains increased in age, the small streams grew into rivers, and as they increased in volume, they also increased in carrying power, and soon they were conveying broken bits of mountain downward, cutting as they went and forming great alluvial fans along the margins of the range.
In a beautiful interrelationship, the mountains continued to push upward at about the rate at which the eroding forces were tearing them down. Had the mountains been permitted to grow unimpeded, they might have reached heights of twenty thousand feet; as it was, the system of balances kept them at some undetermined elevation, perhaps no more than three or four thousand feet.
And then, for some reason, the upward pressures ceased, and over a period of forty million years this once formidable range was razed absolutely flat by erosion, with not a single peak remaining as a memento of what had been one of the earth’s outstanding features. The fabled Ancestral Rockies, a masterpiece of landscape, vanished, its
The time required! The slow passage of years! The constant alterations! Now part of an uplifted mountain, now sunk at the bottom of some sea, Centennial experienced wild fluctuations. Because of the erratic wanderings of the earth, it stood sometimes fairly close to the equator, with a baking sun overhead; at subsequent times it might be closer to the north pole, with ice in winter. It was swamp during one eon, a desert the next. Whenever it came to temporary rest, it should have been exhausted, a worn-out land, but always new energies surged up from below, generating new experiences.
Those lost two billion years lie upon the consciousness of man the way vague memories or ghosts survive in the recollections of childhood. When man did finally arrive on the scene, he would be the inheritor of those vanished years, and everything he did would be limited to some degree by what had happened to his earth in those forgotten years, for it was then that its quality was determined, its mineral content, the value of its soil and the salinity of its waters.
About three hundred and five million years ago occurred what can be called the first event which left an identifiable record at Centennial, and with it our story begins. Within the mantle, forces developed which produced a penetration of the earth’s crust. The basement broke into discrete blocks, some of which were pushed upward higher than their surroundings, to relieve the pressure from below.
The resulting mountains covered much of central Colorado, following fairly closely the outlines that the historical Rocky Mountains would later occupy, and at the conclusion of five or ten million years they constituted a major range.
It was not born in cataclysm. There was no dramatic opening of earth from which fully formed mountains emerged. Nor was there any excess of volcanism. Instead there was the slow, unceasing uplift of rock until the new mountains stood forth in considerable majesty. They were the Ancestral Rockies, and since they left behind them rocks which can be analyzed, we can construct for them a logical history.
They were not soaring peaks, like their successors, but they did rise from sea level and would have seemed higher above their pediment than today’s Rockies, which although they lift far into the sky, take their start from plains already high.
From the moment of their birth they participated in a startling series of events. No sooner had they pushed their crests above the flat surface of the land than small streams began to nibble at their flanks, eating away small fragments of rock and sand. High winds tore at their low summits, and freezing winters broke away protuberances. At intervals earthquakes toppled insecure rocks; at other times inland seas lashed at their feet, eroding them further.
As the mountains increased in age, the small streams grew into rivers, and as they increased in volume, they also increased in carrying power, and soon they were conveying broken bits of mountain downward, cutting as they went and forming great alluvial fans along the margins of the range.
In a beautiful interrelationship, the mountains continued to push upward at about the rate at which the eroding forces were tearing them down. Had the mountains been permitted to grow unimpeded, they might have reached heights of twenty thousand feet; as it was, the system of balances kept them at some undetermined elevation, perhaps no more than three or four thousand feet.
And then, for some reason, the upward pressures ceased, and over a period of forty million years this once formidable range was razed absolutely flat by erosion, with not a single peak remaining as a memento of what had been one of the earth’s outstanding features. The fabled Ancestral Rockies, a masterpiece of landscape, vanished, its
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