16 THE BOOK CLIFFS COAL FIELD. 
MESA VERDE FORMATION. 
Well-exposed sections in the face of the Book Cliffs (Pis. IV and 
X) show that the Mancos shale grades upward into the overlying 
Mesaverde formation with no apparent break in sedimentation. 
The transition is marked by the increasing prevalence of sand in the 
upper part of the Mancos, and in the Book Cliffs field a sharp 
boundary can not be drawn between the formations. The Mesa- 
verde consists of alternating beds of buff sandstone and drab or 
dark shale with workable beds of coal in the lower part (PI. V). 
These are the escarpment-making rocks of the Book Cliffs, and they 
are well exposed throughout the area. 
The sections in Plate VI show the general character of the forma- 
tion. About a third of it is composed of shale, most of which occurs 
in the lower half, while the upper part consists principally of sand- 
stone. The areal distribution of the different strata is varied, and 
no two sections are exactly alike. Some beds of sandstone, however, 
are persistent for several miles. Coal is practically limited to the 
lower 700 feet of the formation, and throughout the field one or more 
beds ranging from 2 to 21 feet thick have been found, as described 
on pages 24-41, wherever prospecting has been done. The shale 
of the Mesaverde formation is commonly sandy and is drab in color, 
but where associated with the coal it is usually carbonaceous. The 
sandstone is generally buff, though occasionally it is almost white, 
and in places red. The bedding ranges from thin to massive, some 
of the layers being only a few inches while others are 50 feet thick, 
the usual thickness being between 2 and 5 feet. The sandstone is 
prevailingly fine textured and is conspicuously feldspathic, consist- 
ing in general of rounded grains of quartz with considerable feldspar 
and subordinate mica. Exposed surfaces are often coated with 
efflorescing salts, and the sandstone locally shows honeycomb weath- 
ering. The rocks of the Book Cliffs coal field are traversed by 
numerous joints, which are prominently developed in the sandstone. 
Two sets, at right angles, are commonly present. 
At many places in the lower part of the formation the sandstone 
is distinctly red. The color is distributed in irregular patches, gen- 
erally, if not always, a few feet above a coal bed, and usually at 
exposed jutting outcrops. There appears to be no difference in 
general composition between the normal buff sandstone and that 
colored red, and the distribution of the highly colored rocks is too 
irregular to be accounted for by differences in original deposition. 
Similar occurrences have been reported from several of the Rocky 
Mountain coal fields, and the color is believed to be due to the 
burning of coal in underlying beds, the formation of the color being 
analogous to that in the burning of bricks. In Horse Canyon, at 
the western limit of the present survey, the coal bed is about 16 feet 
