Noah's Ark

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Geologists agree that Devils Tower was formed by the intrusion of igneous material. What they cannot agree upon is how, exactly, that process took place. Geologists Carpenter and Russell studied Devils Tower in the late 1800s and came to the conclusion that the Tower was indeed formed by an igneous intrusion. Later geologists searched for further explanations.

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In 1907, scientists Darton and O'Hara decided that Devils Tower must be an eroded remnant of a laccolith. A laccolith is a large mass of igneous rock which is intruded through sedimentary rock beds but does not actually reach the surface, producing a rounded bulge in the sedimentary layers above. This theory was quite popular in the early 1900s since numerous studies had earlier been done on a number of laccoliths in the Southwest.

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Other theories have suggested that Devils Tower is a volcanic plug or that it is the neck of an extinct volcano. These explanations are unlikely, however, for there is no evidence of volcanic activity (volcanic ash, lava flows, or volcanic debris) anywhere in the surrounding countryside.

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No one yet has a definite answer as to how exactly Devils Tower was formed, other than that it was an igneous intrusion into the sedimentary layers above and that the molten rock comprising the Tower did not surface.

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In any case, geologists agree that the igneous material intruded and then cooled as phonolite porphyry, a light to dark-gray or greenish-gray igneous rock with conspicuous crystals of white feldspar. As the lava cooled, hexagonal (and sometimes 4-, 5-, and 7-sided) columns formed. As the columns continued to cool, vertical cracks developed as the columns shrank horizontally in volume (see also Devils Postpile National Monument).

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Until erosion began its relentless work, Devils Tower was not visible above the overlying sedimentary rocks. But the forces of erosion, particularly that of water, began to wear away the sandstones and shales. The much harder igneous rock survived the onslaught of erosional forces, and the gray columns of Devils Tower began to appear above the surrounding landscape.

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As rain and snow continue to erode the sedimentary rocks surrounding the Tower's base, and the Belle Fourche River carries away the debris, more of Devils Tower will be exposed. But at the same time, the Tower itself is slowly being eroded. Rocks are continually breaking off and falling from the steep walls. Seldom do entire columns fall, but on rare occasions they do. Piles of rubble - broken columns, boulders, small rocks, and stones - lie at the base of the Tower, indicating that it was, at some time in the past, larger than it is today.

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Recent history

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The Columbia River Plateau lies across parts of the states of Washington, Oregon, and Idaho. During late Miocene and early Pliocene times, one of the largest flood basalts ever to appear on the earth's surface engulfed about 63,000 square miles (160,000 km) of the Pacific Northwest, forming a large igneous province. Over a period of perhaps 10 to 15 million years lava flow after lava flow poured out, eventually accumulating to a thickness of more than 6,000 feet (1.8 km). As the molten rock came to the surface, the earth's crust gradually sank into the space left by the rising lava. The subsidence of the crust produced a large, slightly depressed lava plain now known as the Columbia Basin or Plateau. The ancient Columbia River was forced into its present course by the northwesterly advancing lava. The lava, as it flowed over the area, first filled the stream valleys, forming dams that in turn caused impoundments or lakes. In these ancient lake beds are found fossil leaf impressions, petrified wood, fossil insects, and bones of vertebrate animals.

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The ones in Dinosaur National Park. There's some petroglyphs on a rock somewhere that creationalists claim to have come from the natives who lived there thousands of years ago. Never mind, of course, that Dinosaur National Park is one of the most fossil-laden areas found in the US and that over the past two hundred years there have probably been as many fossil-hunters in the area as scorpions. Also, you'd have to ignore the fact that the petroglyphs look almost exactly like what dinosaurs were thought to have looked like in the late 1800s and early 1900s. Even if the petroglyphs weren't a hoax, chances are they were just some fossil-hunters a hundred years ago who scratched some diagrams on a rock at night beside their campfire.

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The creationalist websites I've seen list the petrographs as "Class C or Class D evidence", not to be repeated or used by creationalists in debates because of the weakness of the evidence.

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