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. ii), 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 Eailroad 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 Eoubideau siding, near milepost 378, the sand- 

 stone that underlies the shale makes its appearance. This sandstone, 

 which contains thin l^eds of coal, has been called the Dakota sand- 

 stone, but the best authorities now place it in the bottom of the 

 Mancos shale, and hence the Dakota may not be present. The rocks 

 rise rather steeply in the direction in which the train is moving, 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 13 



