THE FLEXING ALONG THE FAULT. 59 



The Tertiary movement has not perceptibly influenced or changed the 

 position of the upturned Algonkian strata. It was the reverse of that of 

 the Algonkian, and strata of various degrees of firmness were flexed upward 

 from the east. The massive Tonto sandstone curving slightly downward 

 towards the fault from the west (fig. 10), indicates that a portion of the fold 

 that preceded the Tertiary fault compressed the upturned Chuar shales, but 

 did not materially change their position in relation to the plane of the fault. 



Upper Aubrey 



Lower Aubrey 



Red Wall 



Tonto £ T.sd 



Chuar 



a. 



Figurk 10. — Ideal Section of East Kaibab Monocline. 



Illustrating the position of the strata on the line of sections 4, 5, 6, etc., before the breaking of 

 the monoclinal fold, portions of which are preserved by the Tonto sandstone in sections 5 and 6. 



The evidence of Tertiary flexing is clear and decisive. The massive Red 

 Wall limestone, 900 feet in thickness, curves up and bends over, taking a 

 westward dip, as seen in section 4. All along the line of the fault the sand- 

 stone, limestone and shales approach it at a high angle, and are frequently 

 in a vertical position as well as more or less metamorphosed. The study of 

 the probable conditions under which this upturning of the strata occurred 

 is very interesting, and opens up questions that have a bearing on the history 

 of the erosion of the Grand Canon. 



In the diagramatic section (fig. 11) the relative positions of the Aubrey 

 limestone and sandstone, the Red Wall limestone, and the upper calcareous 

 and lower sandstone series of the Tonto group, are defined on both sides of 

 the fault. Dotted lines indicate the position of the strata on the west side, 

 out to the fault line, prior to their removal by erosion. The Aubrey lime- 

 stone has been eroded away in the immediate vicinity of the fault. The 

 subjacent sandstone approaches nearer, and its upturned massive beds are 

 shown in sections 4, 5 and 6. It is not, however, until the great Red Wall 

 limestone is reached that immediate contact with the plane of the fault 

 occurs. Here there is decided evidence of the lateral and vertical pressure 

 accompanying the displacement. The upper limit of the Red Wall lime- 

 stone has heen displaced, as shown in fig. 11, from x, on the west side 

 of the fault, to x on the east side, a distance of nearly 1,300 feet. This 



