6o6 



ROLLIN T. CHAM BERLIN 



succession of parallel crevasses which point obliquely upstream as 

 they extend in toward the middle of the glacier. Such a belt of 

 crevasses bears some resemblance to the belt of faults in the Lake 

 Basin field. 



The other process which is known to produce results of this 

 kind is torsion. Its behavior has been strikingly illustrated by the 

 famihar experiment of Daubree, who subjected a long plate of 



glass to torsional stress.^ The 

 result was to produce numerous 

 fractures in two distinct sets 

 which crossed each other approx- 

 imately at right angles (Fig. 3). 

 The fractures of each set were 

 nearly parallel to one another, 

 and were inclined approximately 

 at 45° to the axis of torsion. 

 Either set of parallel fractures 

 would look much like the strip 

 of faults in the Lake Basin field, 

 provided the other intersecting 

 set did not form. 



APPLICATION TO THE LAKE 

 BASIN FAULTING 



The most striking character- 

 istic of this belt of faulting in 

 Montana is the grouping of the 

 faults in a long, narrow strip 

 trending W.N.W. and E.S.E. 

 Scarcely less conspicuous is the 

 fact that, almost without exception, the individual fault traces 

 are inclined to the axis of the belt at angles in the general vicinity 

 of 45°. The third fact of prime significance appears to be that 

 toward the west end of the belt the fracturing took place on the 

 south flank of an upHfted tract, while toward the east end of 



'G. A. Daubree, Etudes synthetiques de geologic experimentale (1S79), Tome i, 

 pp. 307-15- 



Fig. 3. — Fractures developed in a 

 glass plate by torsion. The two sets of 

 fractures are nearly at right angles to 

 each other and inclined 45° to the axis 

 of torsion. (From Daubree.) 



