| OCR Text |
Show 256 GEOLOGY OF THE HIGH PLATEAUS. end, where a number of basalt streams appear to have burst out of the western wall near the summit and poured down upon the talus and slopes below. They are of small extent and mass, and are noteworthy-only as an instance of the peculiar positions from which basalt sometimes breaks out. A few miles to the south of the southern cape of the plateau is another small field of basaltic eruption. It is located in the bottom of a rather broad valley or basin. A large cinder-cone is still standing singularly perfect in symmetry and perfect also in its preservation. The cup at the summit is not broken down, but still preserves a continuous rim. From this cone streams of basalt flow southward, and entering a canon in the Jurassic sandstone reach the front of the White Cliffs nearly 12 miles from their source. The individual streams have spread out very thin, and are in some places very slender, with every indication of extreme fluidity at the time of their passage. In the canon the basalt is nearly all swept away by erosion, only a few small patches (in situ) being left to indicate its former existence. But beyond the canon larger remnants are seen, and these evidently formed the terminations of the coulees. It is impossible to affirm anything as to the age of this basalt, though I have little doubt that all the damage it has suffered from weathering and erosion might surely have been accomplished in the period of a thousand years and perhaps in a shorter time. On the other hand, it may be several thousand years since the vent became silent. Four miles to the west of this cone stand half a dozen others, perched high upon cliffs or mesas, and sending their streams into the upper canon of Kanab Creek. These appear to be older and more weather-beaten, though evidently belonging to the most recent geological history of the country. |
