248 • ROLLIN T. CHAM BERLIN 



neighborhood of 45°, and may plunge downward or upward. What- 

 ever fracturing or shearing there be, resulting from these lateral 

 mountain-building thrusts, should follow these dipping-planes as 

 lines of least resistance. If the mass under stress be prevented 

 from undergoing relative motion in these directions, a much greater 

 force would be necessary to compel it to move in any other direction.' 

 Perfectly in accord with these deductions and bearing directly 

 upon the case under analysis, is the experimental work of Daubree 



Fig. 7. — An experiment b)' Daubree. The material of this prism was a carefully 

 prepared mixture of plaster, wax, and resin, molded so as to be as nearly homogeneous 

 as possible. When subjected to direct pressure at both ends, a wedge-shaped mass was 

 fractured loose and lifted slightly out of its bed. Several systems of fractures have 

 developed. 



upon the problem of jointing. This brilliant experimenter subjected 

 blocks of wax to direct pressure operating on the two opposite 

 sides of the block. There were developed in this way two systems 

 of fractures which were inclined to the direction of pressure at angles 

 approximating 45°, and which, at the same time, bear a most striking 

 resemblance to the Appalachian Mountain block ABC developed in 

 Fig. 6. Fig. 7 is copied directly from one of Daubree's plates.^ The 

 two figures form an instructive comparison; the one, developed from 

 an analysis of data collected in the field without forecast of the 

 result; the other, a photographic record of a direct experiment. In 



1 G. F. Becker, op. cii., p. 47. 



2 A. Daubree, Etudes syntheiiqiies de geologic experimentale, T. I, p. 316, Plate II, 

 Fig- 3- 



