8 



GUIDEBOOK OF THE WESTERN UNITED STATES. 



At the loop which the railroad makes before it climbs the eastern 

 front of the mountains there is exposed a dark shale (Benton shale 

 or lower part of the Colorado group), which lies near the base of the 

 Upper Cretaceous series. At Plainview the road cuts through a 

 hogback ^ formed of the upturned edge of the underlying Dakota 

 sandstone and shows some of the variegated sandstone and shale of 

 the Morrison formation, which lies directly below the Dakota sand- 



FiGURE 2. — Dakota hogback and mountain front north of Plainview, as seen from the 

 " Moffat road." The dash line indicates the boundary between the Morri.son formation 

 and the Carboniferous sandstone. 



stone, or toward the mountains. The succession of rocks in the hog- 

 back and the mountain front is shown in figure 2. Beyond the 

 valley formed in the soft rocks of the Morrison formation the red 

 sandstone (Fountain formation) lies upturned against the mountain 

 front in great triangular slabs like the teeth of a gigantic saw. 

 (See PI. Ill, B.) The railroad in climbing the mountain front 

 pierces the projecting points of this hard layer by many short tun- 



Denver itself, but here it is so far 

 below the surface that it has been 

 reached in only the deepest drillings. 

 The coal is mined from slopes which 

 go down on the outcrop of the coal 

 bed or from shafts which are sunk 

 nearer the center of the basin and 

 which reach the coal at different 

 depths. 



The coal is what is now generally 

 called subbituminous, a rank which is 

 below that of the bituminous coals of 

 the East. It is frequently called 

 " black lignite," because of its color 

 and because it has some of the proper- 

 ties of a lignite, or woody coal. The 

 subbituminous coal does not soil the 

 hands and is a desirable domestic fuel, 

 but upon exposure to the weather it 



breaks up or " slacks " — the lumps fall 

 to pieces and the coal becomes a heap 

 of fine fragments. It contains a much 

 higher percentage of water than the 

 eastern coals, and this gives it a much 

 lower fuel value. Notwithstanding 

 these defects, subbituminous coal is 

 extensively mined and finds a ready 

 market throughout the Denver region. 

 * A name applied in the Rocky Moun- 

 tain region to a sharp-crested ridge 

 formed by a hard bed of rock that dips 

 rather steeply downward. One of the 

 best examples of this kind of surface 

 feature can be seen at Canon City, 

 where the Skyline Drive follows the 

 sharp crest of a hogback of Dakota 

 sandstone for miles, as shown in PI. 

 XXXV (p. 73). 



