142 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
As seen in profile the Echo CHffs ^Nlonochne frequently exhibits 
an eastern slope which is almost if not quite as steep as the bold west- 
facing scarp; as seen from the west the crest-line of the cliffs is serrate, 
a succession of sharp peaks or crags, with intervening sags. This 
departure from the normal tabular form of the cliffs is very striking, 
and has been mentioned by Powell, Dutton, and Davis. Powell 
('75, p. 192) relates the peculiar form of the cliffs to the "line of dis- 
placement" in a general way; Dutton ('82, p. 205) considers it the 
effect of "the considerable inclination of the strata"; but Davis 
('01, p. 141-142) suggests that "strike faults with small throw, torn on 
the slope of the monocline," may be responsible for the features 
observed. x\.s has been shown by Davis, the character of the cliffs is 
not due to local increase in the dip of the strata, nor to changes in the 
thickness of the cliff-making sandstones. 
In order to determine whether the back slope of the monocline was 
cut by longitudinal faults Avhich might account for the oversteepening, 
I crossed to the eastern side of the cliifs at three points: first, at a 
point eight miles north of ^Yillow Spring, later at a point a mile or 
two southeast of Cottonwood Tank, and finally at a point five or six 
miles south of Bitter Spring. At the two first points the peculiar 
feature in question was well marked, while at the place of the third 
traverse, the back slope of the monocline was more gentle. In no 
case was any evidence of a fault observed. The sandstone composing 
the upper part of the cliffs is characterized by very pronounced cross- 
bedding having a prevailing, strong dip to the east and southeast. 
Tlhat part of the eastern slope developed on these beds has an inclina- 
tion fairly coincident with the angle of crossbedding. Lower parts 
of the slope, developed on beds which show crossbedding but slightly 
inclined, have a more gentle inclination. Many smaller pinnacles or 
hills formed from the upper beds have a sharply inclined eastern face 
undoubtedly developed on one of the steep crossbedding planes, while 
the pronounced jagged or saw-toothed profile of some of the small 
ridges seems to be traceable to the influence of the same planes of 
weakness. At the northernmost section, where the oversteepening 
of the back slope is not marked, the crossbedding seemed less pro- 
nounced, and the eastward inclination of the laminae less uniform 
than usual. Still farther north, notably between Bitter Spring and 
Echo Peaks, the Echo Cliff's show strongly developed joint structure, 
such as is also visible in the ^>rmilion Cliff's on the opposite side of 
