D. WALCOTT — A DISPLACEMENT IN THE GRAND CANON. 



ami Cwa-gunt valleys. Two Bynclinal folds with a north and south trend, 

 have been crossed and the Bynclinal in which Nun-ko-weap butte res 

 has been entered. North of the latter 1 1 1 « - Btrata dip east and south to the 

 limit of observation at the northern wall of Nun-ko-weap valley. 



From Chuar lava hill, in Chuar valley, north to Nun-ko-weap valley, the 

 pre-Tonto strata rise towards the fault on the west, sometimes to a limited 

 ree, as in Bection s . though more frequently the flexing embraces one or two 

 thousand feel of Btrata thai rise, with a more or less abrupt curvature, from 

 a point half a mile or more west of the fault -< < sections 1. 5 and 6), At 

 the western fault of Bection 1. in Nun-ko-weap valley, the argillaceous shales 

 real against the hard lava-, sandstones and magnesian limestones, ami bear 

 no evidences of metamorphism. In Chuar valley the same thing occurs on 

 the west side of the west branch of the fault ; hut the strata on the east 



side nf the fault, forming the west bIoj f Chuar lava hill (section 8, 1'. 



T. fault i and the strata on the west side of the east branch of the fault 

 sections 8 and '.• I are extensively altered. The lava Hows of the 

 -tern Blope of the hill, with their interbedded and overlying Band- 

 ies, are turned downwards towards the fault. The sandstone is changed 

 to quartzite; the lava is compressed, and so interbedded with the .-ami- 

 ne that the first impression is that a plastic mass ha- hem pn-sed 

 against, and dragged down, the slope. On the east fault, massive layers of 

 sandstone have- been altered to quartzite, and the lava beds curved up as 

 readily a- the more flexible interbedded sandy -hale-. The Btrata against 

 which the metamorphosed beds were pressed, at the time of their metam- 

 orphism, are now concealed by the throw of the fault. Between ( Ihuar lava 

 hill and Nun-ko-weap valley the Tertiary movement has carried the pre- 

 I : strata on the east of the fault entirely out of Bight, bringing 

 Carboniferous strata into contact with the pre-Cambrian Chuar series. 



From these observations it appears that at the close of the pre-Cambrian 

 period of deposition of Bediments in this region, a change ensued that re- 

 sulted in the uplifting, as we now know, of 12,000 feet of Btrata, between 

 the sum mil of tie pre-Cambrian terranes and the A.rchean(?); and also, a 

 considerable portion of the A^rchean (?) to the southwest During this uplift, 

 or possibly later, a fault of considerable importance began on the line .it 

 the pie-, nt Unite fault, displacing the strata with a downthrow to the west 

 «,| from WO to 1,000 feet in the area now exposed to view. Tins movement 

 wa- probably prior to the planing to base level, by erosion, of the inequalities 

 ami irregularities of the Burface produced by the undulations and fault- in the 

 pr< -Tonto formations. The uplifting and metamorphism of the Btrata along 

 the line of the pre-Tonto fault, could scarcely have occurred without the 

 presenct of sufficient superincumbent rock to give the lateral pressure d 

 try to produce the phenomena observed bisections 1 . 1. 5, '''ami 7. 



