36 LEOPOLD REINECKE 



Nor can the lower and flatter of the two ridges be considered a 

 peneplain remnant. Both ridges are, in fact, part of one surface 

 in the stage of early old age, a surface with average slopes of about 

 2\ per cent. Their nearly flat surface is doubtlessly due to their 

 lying between nearly parallel drainage lines. 



Measurements made along apparently flat ridges, moreover, 

 often show that they slope at a quite appreciable rate. The slopes 

 upon St. John ridge, one of the ridges referred to in the preceding 

 paragraph (Fig. 2, profile 3), vary from 100 to 300 feet to the mile. 

 In Fig. 4, an apparently flat sky line is shown between the points 

 a and b which are about 7! and 6 miles respectively, from the 

 camera. From the photographic work done at this place it is 

 known that a vertical shift of T ^ of an inch in the sky line of the 

 picture represents an actual fall of 90 feet in the topography, and 

 that between a and b there is a broad upland draw which is 250 

 feet deep, and whose sides slope at the rate of 100 feet to the mile. 

 If the sky line in Fig. 4 were farther away, it would, without doubt, 

 appear much flatter. In the clear western air, ridges 20 miles 

 away often are plainly visible. 



Discordance of structure and topography: Discordance of 

 topography and structure must also not be considered a final proof 

 that the land form being examined is at all plainlike. Relatively 

 flat surfaces planing across the contacts of rocks of different hard- 

 ness are quite common in the Interior Plateaus, but sloping surfaces 

 which plane across the structure are much more common. The 

 flat areas are local developments on the rolling-hill type of Interior 

 Plateau topography. In one instance a flat surface was seen planing 

 across a centroclinal basin of relatively soft rocks which were pro- 

 tected on the outside by hard layers. The flat surface is shown in 

 Fig. 2, profile 6, just east of the point marked Hamilton Hill, and 

 a part of the same surface in the foreground of Fig. 4. This is 

 undoubtedly a case of local base-leveling and not a proof of uni- 

 versal peneplanation. In another locality a flat ridge top lying 

 next to a large river at an elevation of 3,800 feet was found planing 

 across the structure. The ridge, a part of King Solomon Mountain 

 in the Beaverdell area, is shown in cross-section in Fig. 2, profile 4, 

 but the change of structure is not shown in the profile. This ridge 



