DENVER & RIO GRANDE WESTERN ROUTE. 181 
activity at about this time the lava may have originated there. The 
striking thing about these lava flows is the enormous amount of ero- 
sion that has taken place since they occurred. The date of the flow 
can be fixed only as some time in the Tertiary period, but it was long 
enough ago to permit the removal from the valleys of rocks at least 
a mile in thickness. 
The sandstone and interbedded shale immediately below the lava 
cap in Grand Mesa contain beds of coal and were formerly called the 
Laramie formation, which belongs at the top of the Upper Cretaceous 
series (see table, p. 11), but now they are known to be older and to 
correspond with the heavy sandstones that form the Mesa Verde, in the 
southwestern part of the State, and hence they are called the Mesa- 
verde formation. The same formation carries the coal at Anthracite 
and Crested Butte, northwest of Gunnison, At that place the coal 
beds contain coal of high rank, but in the Grand Mesa, which is far- 
ther from volcanic disturbances, the coal is of much lower rank, most 
of it being subbituminous, or what was formerly called “black lig- 
nite.” A large mine is operated at Somerset, but in that part of the 
mesa which is visible from the river bank west of Delta coal is mined 
only for local use. 
On the left, but not visible in many places, is the broad upward 
swell (anticline) known as the Uncompahgre Plateau, which is com- 
posed of sandstones that underlie the shale seen about Montrose and 
Delta. These sandstones will be seen in the canyon between Delta 
and Grand Junction. Around the margin of the plateau the massive 
red sandstones are deeply cut by the streams which flow from this 
upland in rugged canyons that have nearly vertical walls. These 
canyons are visible from the trains of the Denver & Rio Grande 
Western Railroad from Delta to the Utah State line. The interior 
of the plateau is unbroken and consists of a gently undulating up- 
land without marked surface features. 
Just after passing Roubideau siding, near milepost 378, the sand- 
stone that underlies the shale makes its appearance. This sandstone, 
which contains thin beds of coal, has been called the Dakota sand- 
stone, but the best authorities now place it in the bottom of the 
cos shale, and hence the Dakota may not be present. The rocks 
rise rather steeply in the direction in which the train is egies and 
soon variegated shale and maroon sandstone may be seen. These 
rocks are in part the same as those which the traveler may have seen 
at many places along the Front Range and which contain the huge 
dinosaurs described on page 70. A skeleton of one of these dinosaurs 
was once found across the river from Grand Junction in rocks of the 
Same kind. : 
80697°—22-18 
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