APPENDIX. Ill 



latter a portion of the Desert Province. Both the Plateau sedi- 

 ments and the Desert Range rocks are greatly masked by beds 

 of basalt and other extravasated material. Back and forth across 

 the zone separating the plateaus from the Basin Ranges he passed 

 in long rapid marches, studying now the one, now the other re- 

 gion, and ever examining the volcanic phenomena by which he 

 was surrounded, and yet his keen and well-trained eye caught 

 the more important topographic and geologic features, and he 

 has given in his report a singularly clear and comprehensive ac- 

 count of the region when we consider the circumstances under 

 which it was made. He recognized the principal structural cha- 

 racteristics of the plateaus, and in some instances the structure 

 of the Basin Ranges. He recognized that he was travelling on 

 the border between the two. , He discovered the sequence of the 

 sedimentary groups of the Plateau Province, and collected suffi- 

 cient paleontological evidence to demonstrate his conclusions. 

 He closes this report with the following characteristic and vivid 

 description of the Desert Range Province : " It is a great de- 

 pressed mountainous region, deeply buried beneath the sediments 

 which have been eroded from its own mountains by a surrounding 

 sea. This action has filled the valleys, gradually covered the 

 foot-hills, and, removing the debris from the mountain bases as 

 fast as formed, has left their clean and sharp-cut tops projecting 

 above the surrounding plain without the usual accompaniment of 

 foot-hills and border region which surround nearly all ranges, the 

 changes on the contrary from mountain slope to the gentle incline 

 of the plain being generally very abrupt. The mountains seem 

 to be of ancient plutonic or metamorphic rocks, or else of lavas ; 

 the former more often forming ranges, of which the majority trend 

 about northwest and southeast; the latter more frequently occur- 

 ring as striking isolated peaks. The detrital filling varies from 

 gravels traceable to the rocks of adjacent hills, to the finest of 

 alluvium, the dust of which the winds often carry for miles into 

 Northern Arizona. It is sparsely sprinkled with a dreary vege- 

 tation, composed principally of scattered individuals of many 

 species of mimosas and of cacti, the most striking of the latter 

 being the tall and isolated Cereics giganteus. 



" To stand on the edge of the Pinal Mountains upon a quiet day 

 and look off upon these wonderfully silent and arid plains, with 

 their innumerable 'lost mountains' rising like precipitous islands 

 from the sea, all bathed in most delicate tints, and lying death- 

 like in the peculiar, intangible afternoon haze of this region, which 

 seems to magnify distant details rather than to subdue them, 

 impresses one most deeply. The wonderful monotony seems 

 uninclosable by an horizon ; and one imagines the scene to con- 

 tinue on the same and have no end. Though the gulf and ocean 

 are three hundred miles away, yet here is the continent's real 

 southwestern border. 



(55) 



