24 G. K. Gilbert—The Colorado Plateau Province. 
line bears to the angle or area which it limits and defines. A 
large portion of the Plateau region is divided into great blocks 
—usually a few miles in width and many miles in length—and 
these have been unequally lifted above the ocean which de- 
posited their common sediments, so that each differs from its 
neighbor in altitude. They are bounded by lines of displace- 
ment. The blocks which have been lifted highest have been 
most exposed to erosive agencies, the tendency of which is to 
ideal one, but was carefully drawn to represent a tract of 
country, lying in Utah and Arizona, of which the main geolog- 
ical features are clearly understood. The geological section in 
the foreground is, in the main, the section which is exposed in 
the walls of the Grand Cafion, and is 106 miles long. The 
vertical scale is four times as great as the horizontal. The base 
line marks the level of the ocean, and the dotted line the 
level of the Colorado river. The rock bed marked with small 
ment is 1800 feet. It is known only asa simple fold. Along 
the lines of the first three had the ce wall has 
risen, or the western has fallen; but with the remaining two 
the reverse is the case. 
[To be continued.] 
