DENVER & RIO GRANDE WESTERIST ROUTE. 



199 



Beyond Cisco the railroad ciir^'es here and there over the shale 

 upland, steadily approaching the foot of the Book Cliflfs. (See 

 sheet 8, p. 210.) As it nears the cliffs it seems to be lost in a maze of 

 small shale hiUs, as shown in Plate LXXXII, 5, but in places one 

 may catch glimpses through them of the ragged front of the cliffs. 

 Viewed from a distance the Book Cliffs look like a regular mountain 

 front, but viewed near by they are seen to be made up of a series of 

 terraces or benches, each bench being formed by some hard bed of 

 sandstone more resistant to erosion than the beds above or below. 

 Each bench is cut by streams into a nimiber of salients, or teeth, 

 which project far beyond the main mass of the cliffs. Behind and 

 above the lowest row of salients there may be a second row, formed 



Figure 53. — Mountains carved from a laccolith. The block at the rear shows the former 

 position of the sedimentary beds after they were forced upward by the iuti-usion of 

 the lava. 



by a similar hard bed, and in places there is a still higher row of 

 salients, formed by a third hard bed. The resulting cliffs present 

 a front that is very irregular in detail but very regular when viewed 

 from a distance. A view along the front, showing the lower tier of 

 salients, is given in figure 54:. The lowest bench of the cliffs is 

 formed by the lowest sandstone in the coal-bearing Mesaverde for- 

 mation, and the slope below is composed of Mancos shale. This 

 shale is very homogeneous in composition, and therefore on st€ep 

 slopes it has been cut by many minute ravines, with a wealth of 



the hardened lava is more resistant 

 than the surrounding rock, which has 

 been worn away, it now stands up as 

 a mountain or a mountain range. 



On account of their peculiar method 

 of formation Gilbert proposed for 

 them the name " laccolite " (which 

 was afterward changed to "lacco- 



lith"), meaning stone cistern. Lac- 

 coliths are not only recognized in the 

 western country, but since they were 

 describefl by Gilbert they have been 

 recognized in almost every continent 

 on the globe. A mountain group that 

 has been carved from a laccolith is rep- 

 resented in figure 53. 



