OCCURRENCE OF COAL. 23 
plateau. Northwest of Thompsons, to the end of the area examined, 
the influence of the San Rafael Swell is felt and the dips are north- 
eastward from 2° to 10°. 
The rocks in the Book Cliffs are conspicuously jointed, two sets at 
right angles being well developed, one of which usually is parallel 
to the face of the cliffs. The escarpment is gradually being worn 
back by blocks of sandstone breaking along these cracks and falling 
down to the base of the cliffs. 
Large faults have not been observed in the Book Cliffs coal field, 
but several small dislocations were found in the face of the escarp- 
ment, a few of which will be mentioned. Between Sunnyside and 
Woodside the coal in the face of the cliffs is so distinctly offset that 
a fault can be seen at a distance of several miles, and there are several 
other faults in this vicinity. About 10 miles north of Woodside 
the plane of one fault strikes N. 65° W. and the displacement amounts 
to 120 feet. Another fault in the cliffs 3 miles northeast of Wood- 
side strikes N. 75° W. Here the displacement is only about 20 feet, 
but the fault is clearly exposed, for it involves a bed of coal and the 
strata are bent along the plane of dislocation. There is also a small 
development of breccia. Another fault is clearly exposed in the 
canyon 2\ miles below Carbonera. (See PI. II, B.) There the fault 
strikes N. 75° E. and the throw amounts to about 50 feet. 
COAL. 
GENERAL STATEMENT. 
Coal of commercial importance occurs in the lower part of the 
Mesaverde formation at various horizons from 35 to 700 feet above 
its base. In some localities several beds are present, while in others 
only one or two have been found, but no single bed has been traced 
continuously for more than a few miles. (See PI. VI.) So little 
prospecting has been done that an unqualified statement can not be 
made, but so far as known one or more workable beds are present 
throughout the field here considered. The thickness of the coal 
ranges from a maximum of 21 feet down to mere films of carbonaceous 
matter. The beds outcrop in the face of the Book Cliffs commonly 
100 feet or more above their bases, and at distances from the Denver 
and Rio Grande Railroad which vary from close proximity to a 
maximum of about 15 miles. The dip is at a low angle northward 
and the coal underlies an immense area north of the cliffs. The coal 
is of good quality and compares favorably with that from the Rocky 
Mountain fields. It is but little prospected, however, and there are 
only four small mines with railroad connections between Grand River 
and Sunnyside. 
