34 LEOPOLD REINECKE 



elevations, each being separated from the next by a shorter and 

 steeper slope. Further study proved that a number of flat hill- 

 tops in this region, which have for a long time been regarded as 

 residuals of a tilted peneplain formed by subaerial erosion, were in 

 reality parts of a series of wave-cut marine terraces. 



b) The measurement of slopes and the study of profiles were 

 found very useful in determining the number of cycles of erosion 

 through which the uplands of the Interior Plateaus of British 

 Columbia had passed. The older uplands and younger valley 

 cycles were separated with comparative ease, but detailed study of 

 the slopes was needed to show that no remnants of an older plain- 

 like surface existed within the upland itself. 



c) The measurement and recording of regional slopes will be 

 of the greatest value, however, in cases where old surfaces and their 

 residuals are used to determine the manner in which earth move- 

 ments have taken place or the amount through which a section of 

 the crust has moved. The manner in which movements of the 

 crust have taken place sometimes can be brought out by profiles 

 (see Fig. 2, profile 6), but it is necessary to determine the original 

 internal relief and average slope of an elevated or warped old 

 erosion surface before such a surface can be used for quantitative 

 measurements of movements of the earth's crust. 



In the uplands of the Interior Plateaus, for instance, the relative 

 relief of points within 10 miles of each other quite commonly is 

 from 1,500 to 2,000 feet. If such a surface be uplifted and dis- 

 sected until only remnants of it remain, the difference of elevation 

 between them could be 1,500 feet without the section of the crust 

 within which they occur having been either warped or tilted. Cal- 

 culations of earth movements based on the assumption that such 

 a surface was plainlike before uplift would be liable to errors of 

 1,500 feet or more. If the slopes are not measured, however, old 

 surfaces of marked relief are likely to be thought nearly flat or of 

 much lower relief than actually is the case. For instance in 

 describing an old erosion surface in the Colorado Front Range, 

 Davis 1 says: "In the highland west of Palmer Lake, between 

 Denver and Colorado Springs the sky fine seems to be essentially 



1 W. M. Davis, "The Colorado Front Range," Ann. Assoc. Am. Geog., I, 42. 



