56 C. R. Lougicell — Geology of 



cut and modified by a number of normal faults. This 

 folding continues into the Black Mountains, and hence 

 there is no definite structural division between the two 

 mountain groups. 



Northern division. — Xorth of Callville Mountain the 

 outcrops of Mesozoic formations have the shape of a 

 large letter ^'L'', due to the intersection of two anti- 

 clines at nearly right angles. In the Narrows anticline 

 the beds have been tightly compressed and overturned to 

 the east, and a large strike fault has caused a duplication 

 of formations at the surface. East-west faults have fur- 

 ther complicated the structure, and near the Arrowhead 

 road the Kaibab and Moenkopi limestones have been 

 thrust over Jurassic sandstone, probably in connection 

 with the Callville Mountain overthrust. The Arrowhead 

 anticline is a broad asjmmietric fold w^hich plunges be- 

 neath the intermontane clays at the east end, and at 

 the west dies out as it meets the stronger fold from the 

 north. The Overton and Horse Spring beds are involved 

 in the Arrowhead fold, and near the Narrows of Muddy 

 Creek they are moderately folded parallol to the Nar- 

 rows anticline. Numerous minor faults affect all for- 

 mations. 



Central Division. — On the north side of Callville 

 Mountain, Devonian and Carboniferous limestones lie 

 at an elevation many hundreds of feet higher than 

 adjacent Mesozoic sediments, and the fault plane be- 

 tween formations shows large downthrow on the south, 

 indicating that the older rocks were once in an even 

 higher jDosition with respect to the younger. This re- 

 lation suggests overthrusting, and north of Muddy 

 Peaks the actual thrust plane is well exposed. De- 

 vonian limestone lies on the Jurassic sandstone, and 

 the contact is marked by a smoothly polished surface, 

 above which the limestone is intensely shattered through 

 a thickness ranging from 100 to 500 feet. This shat- 

 tering is also conspicuous along the north base of Call- 

 ville Mountain. The vertical displacement due to the 

 overthrust is at least 9,000 feet, and yet the thrust plane 

 is practically parallel to the bedding. This fact sug- 

 gests that the movement affected a large area. Crum- 

 pling and minor thrusting indicate that the direction of 

 overthrusting was from southwest to northeast. Evi- 

 dently that portion of the block which formerly lay north 



