BRANCHING OF THE FAULT. 



55 



and the strata on the east of the fault are flexed up on each side towards it ; 

 the Chuar strata were turned up in the downward throw, to the west, in 

 pre-Cambrian times, and the Tonto, Red Wall and Aubrey rocks by the 

 eastern throw in the movement producing the East Kaibab displacement. 

 In several localities this has resulted in bringing the soft calcareous and 

 argillaceous shales of the Chuar and Tonto groups side by side (fig. 7), 

 and, as both are nearly vertical, no line of demarkation is observable al- 

 though in the interval between the deposition of the argillaceous shales of 

 the Chuar group and the bringing of the shaly calciferous beds of the Tonto 

 into their present relations to them, upwards of 16,000 feet of sediments 

 were deposited in the Colorado basin, and the geologic history of the greater 

 portion of the North American continent was written. 



The general direction of the fault has thus far been to the south-southeast. 

 Midway between the Kwa-gunt and Chuar valleys it curves more to the 

 southeast and then to the south, scarcely deviating from a north and south 

 line until it reaches Chuar lava hill, where it forks. The east branch passes 

 north of the hill. It crosses the Colorado river in a southeasterly course and 

 runs out a short distance up a side canon. Here the upper Tonto and Red 

 Wall terranes arch over it in an unbroken monoclinal fold although, but a 

 short distance away to the northwest, the massive Tonto sandstone is dis- 

 placed by a downthrow of 400, feet to the northeast. The west branch of 

 the fault continues south a mile or more and then bends to the southeast, 

 crosses the river and disappears beneath the Tonto terrane, displacing the 

 Grand Canon and Chuar groups, but scarcely breaking the Tonto beds. 

 The Tertiary movement appears to have followed the east branch ; this is 

 shown by a cross-section of Chuar lava hill that cuts across the two branches 



West 



East. 



F.T. 



Figure 8. — E. N. E. and W. S. W. Section through Chuar Lava Hill. 



T. Sd.=Lower massive Tonto sandstone; C.=Chuar shales; G. C.=Grand Canon shaly sand- 

 stones. The dip of the latter is the same as that of the lava beds (L) and the Tonto sandstone. 

 a, a=East branch of fault ; P. T.=West branch, and pre-Tonto fault. The western fault cuts through 

 the lava bed and separates the western portion which is part of the highest lava bed brought down 

 by the westward throw of the fault. The fault at this point is not shown in the figure. 



of the fault (see fig. 8). One mile south of this section, on the west 

 branch, the Tonto sandstone is not displaced by the fault, although the pre- 

 Tonto throw, to the west of the strata of the Grand Canon group, is from 



