A PECULIAR BELT OF OBLIQUE FAULTING 609 



will be produced. This would be the set at right angles to those 

 actually occurring in the Lake Basin field. 



Becker has also stated that, if due to torsion, each master 

 fault will be a reverse fault, and the fissures will gape from the 

 start.^ Examination of the fracture planes in the paraffine tests 

 revealed the fact that many of them were straight across or, ex- 

 pressed in terms of structural geology, were vertical faults. In 

 others the fault surface was somewhat incHned from the vertical, 

 or was vertical for a portion of the distance and then curved. 

 Where the fault plane was incHned from the vertical the relations 

 were, as Becker has stated, those of a reverse fault. The hanging 

 wall was elevated with respect to the foot wall. The paraffine 

 tests also confirmed Becker's statement that the fissures will gape. 

 This does very well in an experiment where the weight of materials 

 plays no important part. But reverse faults which gape would be 

 a curiosity in the earth. While in the earth, just as in the experi- 

 ment, the twisting would tend to cause this relation, on the other 

 hand the gravity of the earth, in co-operation with the tension 

 developed by the torsion, should offset this tendency. If the 

 twist developing such a series of parallel faults were accompanied 

 by much tension, downsliding of the blocks should be expected. 

 As there seem to be special grounds for expecting tension, inde- 

 pendently of the torsion, in the case under consideration, reverse 

 faulting as the dominant type in this particular strip in Montana 

 would seem unlikely. 



Furthermore the strains developed by the doming process above 

 outHned would, in all probabiHty, not be of a very intense sort 

 unless there were also counterpart downwarping north of the Big 

 Horn uplift and a depression of the basin south of the Big Coulee- 

 Hailstone dome to complete the twist. Some depression of the 

 basins seems likely, but the twisting was probably not violent. 

 Hence the fracturing, so far as due to torsion alone, should be not 

 far from vertical, and the tendency toward reverse faulting would 

 be slight. Nevertheless in this connection it is interesting to note 

 that reverse faults actually do occur in one section of the fault belt 

 under consideration.^ Normal faulting, however, dominates. 



' G. F. Becker, op. cit., p. 137. " E. T. Hancock, op. cit., p. 140. 



