720 J. H. GARDNER THEJ MlD-COI^TlNENT OIL FIELDS 



In this connection it is suggested as probable that the movement pro- 

 ducing local folds of this type has acted from below, although it must not 

 be understood that they are results of intrusives, nor that they are lacco- 

 litic in origin. But it is believed that the total thickness of the sedi- 

 mentary strata are folded, the first yielding having been in the profound 

 depths. This presupposes a deep-seated transmission of pressure through 

 the zone of flowage. 



In the case of mountain development such a flowage took place on a 

 large scale. The crystalline rocks of the Ozark, the Arbuckle, and 

 Wichita Mountains, the Llano-Burnet region of Texas, or of the Eocky 

 Mountains, have risen from beneath the sedimentary series, due to iso- 

 static adjustment on a large scale. At the time these major stresses 

 were acting on the earth's crust the zone of flowage transmitted pressure 

 more or less equally in all directions, so that the abysmal magma moved 

 laterally to the region of least resistance; but in so doing the overlying 

 rocks had to bear strong hydraulic forces acting upward, and at points 

 where the total strength- of the overlying section was not competent to 

 withstand this pressure there was a local buckling of the whole lithosphere. 



Well logs show that the folds of the Mid-Continent region do not grow 

 less in strength with depth, but, on the other hand, the deeper sands show 

 the sharpest dips. The Bartlesville sand at Gushing, Oklahoma, shows 

 stronger structure at 2,600 feet in depth than does the Layton sand at 

 1,400 feet. Contours on the Tucker sand, below the Bartlesville, show 

 the folds to be even stronger. In 40 feet of surface dip on a limestone 

 at Augusta, Kansas, the oil sand at 2,400 feet in depth dips 80 feet. 

 Similar conditions exist at Blackwell and Healdton, Oklahoma, and are 

 in fact the rule rather than the exception throughout the Mid-Contineut 

 fields. 



