Mesozoic and Ccunozoic Geology and PaUvontolo'jy. 171 



The width of this valley may be about 30 miles, and its whole length 

 about 90, as it stretches away westwardly towai'd the base of the 

 gloomy and dark range of mountains known as the Black Hills. Its 

 most depressed portion, 300 feet below the general level of the surround- 

 ing countr}', is clothed with scanty grasses, and covered by a soil 

 similar to that of the higher ground. 



To tlie surrounding country, however, the Mauvaises Terres present 

 the most striking contrast. From the uniform, monotonous, open 

 prairie, the traveler suddenly descends, one or two hundred feet, into a 

 valley that looks as if it had sunk away from the surrounding world, 

 leaving, standing all over it, thousands of abrupt, irregular, prismatic, 

 and columnar masses, IVequenth^ capped with irregular pyramids, and 

 stretching up to a height of from one to two hundred feet or more. 



So thickly are these natural towers studded over the surface of this 

 extraordinary region, that the traveler threads his way through deep, 

 confined, labjn'inthine passages, not unlike the narrow, irregular streets 

 and lanes of some quaint, old town of the European continent. Viewed 

 in the distance, indeed, these rocky piles, in their endless succession, 

 assume the appearance of massive, artificial structures, decked out with 

 all the accessories of buttress and turret, arched doorway and clustered 

 shaft, pinnacle, and finial and tapering spire. 



One might almost imagine oneself approaching some magnificent 

 city of the dead, where the labor and the genius of forgotten nations 

 had left behind them a multitude of monuments of art and skill. 



On descending from the heights, however, and proceeding to thread 

 this vast labyrinth, and inspect, in detail, its deep, intricate recesses, 

 the realities of the scene soon dissipate the delusions of the distance. 

 The castellated forms, which fancy had conjured up have vanished; 

 and around one, on every side, is bleak and barren desolation. 



Then, too, if the exploration be made in midsummer, the scorching 

 rays of the sun, pouring down in the hundred defiles that conduct the 

 waj^farer through this pathless waste, are reflected back from the white 

 or ashcolored walls that rise around, unmitigated by a breath of air, 

 or the shelter of a solitary shrub. 



The drooping spirits of the scorched geologist are not permitted, 

 however, to flag. The fossil treasures of the way, well repay its sul- 

 triness and fatigue. At every step, objects of the highest interest 

 present themselves. Embedded in the debris, lie strewn, in the 

 greatest profusion, organic relics of extinct animals. All speak of a 

 vast fresh water deposit of the early Tertiary period, and disclose the 

 former existence of most remarkable races that roamed about in by- 



