INTRODUCTION. ll 
“From the high prairies that rise in the back-ground, by a series of terraces 
towards the spurs of the Rocky Mountains, the traveller looks down into an exten- 
sive valley, that may be said to constitute a world of its own, and which appears 
to have been formed, partly by an extensive vertical fault, partly by the long con- 
tinued influence of denudation. 
“The valley is about ninety miles in length, and thirty in breadth, and stretches 
away, westwardly, towards the base of the dark gloomy range of mountains, the 
Black Hills. Its most depressed portion is about three hundred feet below the 
general level of the surrounding country, and is covered by a soil, similar to that 
of the higher ground, supporting scanty grasses. 
View of the Mauvaises Terres.—From the Geological Report of Dr. Owen. 
“To the surrounding country, however, the Mauvaises Terres present the most 
striking contrast. From the uniform, monotonous, open prairie, the traveller sud- 
denly descends, one or two hundred feet, into a valley that looks as if it had sunk 
away from the contiguous world; leaving standing, all over the surface, thousands 
of abrupt, irregular, prisniatic, and columnar masses, frequently capped with irre- 
gular pyramids, and extending to a height of one or two hundred feet, or more. 
“So thickly are these natural towers studded over the surface of this extraor- 
dinary region, that the traveller threads his way through deep, confined, labyrin- 
thine 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 struc- 
