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 '65 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 sides— south, west, and east— 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 far 

 as known, possesses structural and topographical features which distinguish 

 it from the others.* The easternmost division he has named the Park Prov- 

 ince. It is characterized by lofty mountaiin 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 loci,-f 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, aiising from the 

 decreasing frequency of the greater displacements or diff"erential vertical 

 movements of the earth's surface; but such movements as have occurred 

 have been vast in extent and involve greater masses, though the displace- 

 ments have been fewer in number. Great blocks of country have been 

 lifted with a singular uniformity with comparatively little flexing and with 



* Geology of tlio Uiuta Mouutaius. J. W. PowoU. 



t ThiH asHunii)tiou may bo regarded as gcuerally true for Palaiozoric and Mesozoic beds, but not for 

 Cenozoic. 



