MISCELLANEOUS 445 



Miscellaneous Photographs 

 Experiments of Bailey Willis in 1890 in Folding Loaded Strata by Horizontal Thrust 



The following photographs are selected from a series representing models of 

 folded strata. Negatives in United States Geological Survey. Mostly 18 by 24 

 inches. Price, 75 cents each, unmounted; $1 mounted on card or muslin. They 

 should be ordered by model letter : 



The folds are the results of horizontal pressure applied to the ends of flat strata 

 which were confined on four sides and at the bottom, and could rise only by lift- 

 ing a load of bird shot. 



The materials composing the models were mixtures of plaster of Paris and 

 beeswax and Venice turpentine in varied proportions, which resulted in strata 

 of varied plasticity. 



Each pile of strata was compressed from two to five times and photographed at 

 each stage of compression. The photographs therefore represent successive stages 

 in the development of folds and faults. 



1360. Model (no letter). Initial form not shown, all the strata having been laid 



flat. Illustrates the development of original and consequent folds in rela- 

 tively hard strata on a soft base. 



1361 . Models A and C. Illustrate the development of anticlines at points of initial 



dip. The bedded materials are the same in F and C, in both being rela- 

 tively hard and rigid. This is shown in the acute broken folds. The 

 base is soft. Compare E and G. 



1362. Model E. Illustrates development of a primary anticline at a point of initial 



dip near the applied force, together with the growth of a consequent fold. 

 The bedded materials are softer than in model F. Compare G. 



1363. Model E 1. Illustrates the development of 3 anticlines, two of which devel- 



oped at points of initial dip remote from the applied force. The third 

 grew near the applied force iu consequence of swelling of the soft base. 

 The materials are the same as in model E. Compare Gl. 



1364. Model G. Illustrates the growth of folds from an initial form like Model E, 



but in softer materials. 



1365. Model G 1. Illustrates the growth of folds from an initial form like E 1, but 



in softer materials. 



1366. Model H. Illustrates the development of anticlines from a form like G 1, 



but with a softer base beneath the bedded materials. 



1367. Model K. Illustrates the effects of compressing conformable strata accumu- 



lated in a deep syncline of deposition, there being a controlling compe- 

 tent stratum and thin-bedded strata of softer and harder substances which 

 developed minor folds and thrusts. 



1368. Model L. L is the complement of K, being similar in form and materials, 



but having been shortened from the opposite end. The applied energy 

 was used up in developing the folds, and did not affect the distant initial 

 dips. 

 1369-1371. Model M. Illustrates the development of diverse structures in two com- 

 petent series, one at the base and one at the top, and in the intermediate 

 soft incompetent material. 



LXIV— Bull. Geol. Soc. Am., Vol. 13, 1901 



