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Show THE THREE GEOLOGICAL PROVINCES. 5 rolling prairie of its broad expanse to make it as cheerless and repulsive a locality as can well be conceived. But south of the Awapa stands the grandest of all the High Plateaus, the Aquarius. It is about 35 miles in length, with a very variable width, and its altitude is about 11,600 feet. Its broad summit is clad with dense forests of spruces, opening in grassy parks, and sprinkled with scores of lakes filled by the melting snows. On three sidesâ€"south, west, and eastâ€"it is walled by dark battlements of volcanic rock, and its long slopes beneath descend into the dismal desert in the heart of the " Plateau Country." THE THREE GEOLOGICAL PROVINCES. For convenience of geological discussion, Professor Powell has divided that belt of country which lies between Denver City and the Pacific and between the 34th and the 43d parallels into provinces, each of which, so fax as known, possesses structural and topographical features which distinguish it from the others.* The easternmost division he has named the Park Province. It is characterized by lofty mountain ranges, consisting of granitoid and metamorphic rocks, pushed upward and protruded through sedimentary strata, the latter being turned upwards upon the flanks of the ranges and their edges truncated by erosion. The general transverse section presented by these ranges, on the assumption that the sedimentaries prior to uplifting extended over their present locirf is that of a broad and extensive anticlinal sometimes profoundly faulted parallel to the trend, the sedimentary strata which may once have existed being removed by erosion. The intervening valleys still retain the sedimentary series, including the Tertiary beds. This form of mountain structure, with its resulting topographical features, gradually passes as we proceed westward into another type, arising from the decreasing frequency of the greater displacements or differential vertical movements of the earth's surface; but such movements as have occurred have been vast in extent and involve greater masses, though the displacements have been fewer in number. Great blocks of country have been lifted with a singular uniformity with comparatively little flexing and with * Geology of the Uinta Mountains. J. W. Powoll. t This assumption may be regarded as generally true for Palaiozoric and Mesozoic "beds, but not for Cenozoic. |