200 GUIDEBOOK OF THE WESTERN UNITED STATES. 
detail that is amazing to one unaccustomed to the effects of the erosion 
of rocks in a semiarid region. What infinite pains Nature appar- 
ently takes even in carving one of these commonplace hill slopes! 
This carving is, indeed, a work of art comparable to that of the most 
skillful ‘sculptor. 
As the traveler goes westward he finds many shale ridges, which 
form the divides between parallel stream valleys that head in the 
Book Cliffs. These ridges have either flat tops or tops that slope 
regularly away from the front of the cliffs. The tops of the ridges 
stand from 80 to 100 feet above the general level of the plain and 
doubtless represent the surface of a former plain that stood that dis- 
tance above the present surface. When that plain existed the streams 
Figure 54.—Projecting point of the lower salients of the Book Cliffs. View looking east 
from Thompson, Utah. 
could not cut deeper into it, and so the land was reduced to a gentle 
slope, but later the streams acquired greater cutting power and they 
have succeeded in eroding away most of the old plain except where 
it is best protected on the divides. What caused the increased cut- 
ting power of the streams is a difficult question to answer. It may 
have been an uplift of the country, or it may have been a change in 
climate by which the volume of water carried by the streams was 
greatly increased. 
After the train has passed through cuts made in two or three of 
these shale ridges it reaches the village of Thompson, or, as it was 
formerly called, Thompson’s Springs, a name ap- 
oes 2 plied to it. because 5 miles up the canyon that opens 
Population sé. this place there are several springs which have 
Denver 528 miles. | been of great value. In a dry country all settle- 
ment except on the railroad depends on the pres- 
ence of water, and in the early days Thompson’s Springs were the 
chief source of supply for those who were forced to make the trip 
across this inhospitable country. When the railroad was built the 
springs were equally valuable as a source of supply for the locomo- 
Thompson. 
