5IO 



R. T. CHAM BERLIN AND F. P. SHEPARD 



Wedge faults. — The phenomena of wedge faulting occurred rather 

 frequently in the models. These faults, however, were of rather 

 small displacement because it is not easy for the wedges to move 

 for any great distance under the conditions of the experiments 

 without having the whole mass broken across by a general thrust 

 fault. 



Fig. 1 6. — Top layer faulted while bottom layer merely folded. Opposite sides of 

 same model. A section cut through the middle of the model showed more shortening 

 in the two lower layers. The nature of the deformation changed rapidly from place 

 to place. Two stages of faulting, an overthrust on one slope and an underthrust on 

 the other; then reversal of the process. 



Angles of thrust faults. — In considering the angles of thrust 

 faults, W. H. Bucher in his recent paper on "The Mechanical Inter- 

 pretation of Joints" lays great emphasis on the plasticity of the 

 deformed material and the depth at which it is deformed.^ Engi- 

 neering experiments illustrate clearly that the angle of fracture 

 depends on the nature of the material deformed, and in nature the 

 angle of thrust faulting presumably should be influenced by this 

 factor. If nothing else influenced the angle, low-angle faulting 

 might be found where deformations occurred near the surface and 

 where the formations were brittle. High-angle faults should be 



' W. H. Bucher, Jour, of Geol., Vol. XXVIII (1920), pp. 707-30, and Vol. XXIX 

 (1921), pp. 1-28. 



