DENVER & RIO GRANDE WESTERN ROUTE. 191 
| Although the shale which forms the valley that the traveler has 
been following from Grand Junction to this place, if he came over 
the main line, or from Montrose, if he came over the narrow-gage 
line, continues along the foot of the Book Cliffs to the region beyond 
Green River in Utah, the railroad does not follow it because near 
the State line it ceases to form a valley and the outcrop is rough and 
is broken by stream valleys that cross it. In order to avoid this 
rough country the railroad turns to the south (left) soon after leay- 
ing Mack and follows the river through Ruby Canyon for a distance 
of more than 18 miles. The gap in the ridge through which the rail- 
road reaches the river can be seen on the left from the station. 
Half a mile beyond Mack the railroad swings sharply to the 
south (left) and leaves the shale valley. It cuts through the sand- 
stone rim that bounds the valley on the south nearly at right angles, 
disclosing the sandstones and variegated shale beds that underlie 
the dark shale (Mancos) of the main valley. The first sandstone 
to be seen is the Dakota, the lowermost formation of the Upper Cre- 
taceous. Underlying the Dakota is the McElmo formation, equiva- 
lent to the upper part of the Gunnison formation, which has already 
been seen at a number of places. The McElmo formation has every- 
where about the same character and when once recognized is easily 
identified wherever it is seen. It includes an.upper member 150 
feet thick—the one that is first seen after leaving Mack—composed 
of variegated shale and sandstone, which on account of its relative 
softness weathers back into gentle slopes. The underlying member 
is about 60 feet thick and consists mainly of sandstone, which is more 
resistant to weathering than either the overlying or the underlying 
shale and therefore stands out and makes terraces or benches on the 
hillsides. The sandstone is in turn underlain by a gray clay or 
shale, which has a thickness of about 100 feet. These rocks form the 
canyon walls for a distance of about 2 miles, but they are so soft 
that in no place are the walls very steep. Owing to the red and 
green tints, the color effect is rather pleasing, but it soon becomes 
monotonous, and some other color or larger masses of color would 
make a welcome change. 
easily mined with a hand pick and is 
Placed in large bags to be hoisted to 
the surface ready for shipment to mar- 
Ket. The veins are rarely more than 
vent fire, for the gilsonite dust is ex- 
tremely explosive. No artificial lights 
are used in the mines, even at great 
depths. 
The entire gilsonite output of Utah 
(about 20,000 tons annually) is hauled 
over the narrow-gage Uintah Railway 
to Mack, where it is reloaded to the 
larger cars of the Denver & Rio Grande 
Western Railroad. 
Gilsonite is extensively used in the 
manufacture of paints, varnishes, roof- 
ing materials, and rubber substitutes. 
