44 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
strata occurred beneath the harder strata which cap the escarpment; 
but we found no sufficient indication of such weak strata, for the 
base of the escarpment is made chiefly of quartzitic beds which 
stand out in abundant outcrops. 
The Smoothback mass is also a simple east-dipping monocline for 
the most part, but on its southern side a dip of 15° or 20° to the south- 
east is developed; and as a result the gray-and-slate colored cliffs 
which crown the escarpment along this quarter of the range, as well 
as farther north, descend to the mountain base at the north end of the 
Sawtooth mass, and the Trilobite shales make an oblique, northeast- 
southwest depression across the range between its two southern quart- 
ers and open a broad gap in its western face. Curiously enough, a 
sharp notch is cut east and west into the descending part of the gray- 
and-slate escarpment, shown in front view in figures 19 and 22, and 
Fig. 22.— General view of the western escarpment of the Sawtooth mass. The 
piedmont fans (somewhat exaggerated in size) have Bonneville shorelines and 
in side view in Plate 3, A, and in figure 25; and through this notch 
the southern of the two roads ascends from the basin of Tule flats to 
the oblique depression and pass formed by the Trilobite shales. The 
notch and the absence of the upper limestones from the Smoothback 
mass are peculiar features, not to be explained by a one-cycle carving 
of a simple monocline, but easily explained by erosion in two cycles. 
The Sawtooth mass continues the southeast dip which began on 
the southern side of the Smoothback mass, and as a result the scarp- 
making edges of the harder layers here run obliquely across the back 
slope of the range: they may be easily traced from their first appear- 
ance low down at the eastern base, through their gradual ascent south- 
westward to the range crest, although they are more or less interrupted 
by deep valleys. About the middle of this mass intrusive granite re- 
places the stratified series over several square miles of highland, as 
shown in figure 20, and occupies part of the western escarpment, as 
