224 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
so far as we have observed it in the field, consists chiefly of the old fault, 
with the newer displacement greatly diminished. 
Near Coal spring, for instance, we found no signs of a recent fault ; 
but beneath a protecting basalt cap that forms a promontory in the Hur- 
ricane ledge there was displayed a portion of the old fault line. The lava 
rests on a nearly level surface that horizontally truncates the old fault. 
Beneath the black cap the red Moencopie shales on the downthrown 
western side of the fault butt against the gray Aubrey limestone on the 
east of it. 
The amount of dislocation shown by this relation of strata is about six 
hundred feet, and is much less than the throw of the old Hurricane fault 
Figure 4. 3 
The Hurricane fault at Coal spring. 
farther north. That this is not a recent fault is demonstrated by the 
surface on which the lava lies. This, as will be seen later, furnishes evi- 
dence of a long period of erosion that reduced this part of the country 
nearly to base-level before the more recent faulting took place. 
Hardly less apparent than the Coal spring exposure, and certainly 
more striking because of its greater complexity, is the fine cross-section 
on the Hurricane just southwest of Gould’s ranch. Here a section about 
a mile long contains a record of the ancient faulting, the succeeding long 
period of erosion, the basalt flows, the second or modern faulting, and 
recent erosion (see Plate 7, section G-H). The observer, from one of the 
little lava mesas that overlook the Hurricane ledge, sees directly at his 
feet the red and gray Moencopie shales sloping steeply down to the top of 
the cliff proper, which consists of hard Aubrey limestone, and drops down 
abruptly one thousand feet. At the base of the Aubrey cliff, or fourteen 
