GENERAL FEATURES. 3 



There are many parts of the interior area that recall the mountain 

 scenery of northern New York and New England, and the general char- 

 acter of the region is exceedingly broken and rugged. 



Having passed the barrier of foot-hills surrounding the Black Hills, 

 and having traversed the broad, red valley that encircles them as a moat, 

 one gradually ascends the outer slope of the Hills and soon enters, at an 

 altitude of 4,500 or 5,000 feet, the wooded portion of the region. This 

 outer slope varies greatly in width, and is underlaid by the older sedi- 

 mentary rocks, cut in almost every direction by narrow and deep canons. 

 Usually from the broken interior edge of this slope or plateau of sedi- 

 mentary rocks one descends a bluff or escarpment and enters the central 

 area of slates and granites, which is tossed into high ridges and sharp peaks, 

 cut up by narrow and deep valleys and ravines, and generally thickly tim- 

 bered with the common pine of the Rocky Mountains (Pinus ponderosa). 



In the structure of the Hills there are many points that make them 

 a miniature representative, compact and wonderfully complete within them- 

 selves, of the topography and geology of the great Rocky Mountain sys- 

 tem. In their interior area of sharp ridges of schist and slate and ser- 

 rated peaks of granite are represented the character and structure of a 

 large portion of the nucleal regions of the Rocky Mountains ; and in the 

 surrounding sedimentary strata we have, exhibited in a beautifully clear 

 manner, some of the most interesting features of the composition and 

 structure of the sedimentary formations of the Far West. 



To the geologist the detailed study of their rocky structure presents 

 many points of exceeding interest, and, unlike the volume in the East 

 which is so generally concealed with heavy covers of drift or soil, he has 

 here the pages of the geological record plainly spread before him, with no 

 concealing surface accumulations, and with the intimate structure plainly 

 revealed by bluffs and numerous cross-cutting canons. 



The results of the geological observations, which were as carefully 

 made as the limited time and rapid work of the exploration would permit, 

 will be given in a somewhat detailed manner in Chapter III. Our small 

 collections of fossils were made from formations so wonderfully rich that 

 Professor Whitfield has been enabled to prepare a most important mono- 



