6o6 WILLIAM J. MILLER 



zones are very irregular, while in nature they are usually very regu- 

 lar, or even straight, for long distances; (3) such regular surfaces 

 could hardly have resulted from vigorous current scour because the 

 contorted zones are usually remarkably uniform in thickness for 

 long distances; (4) there is almost invariably no evidence for the 

 present or former existence of materials of such arrangement and 

 character directly over the contorted zones as to give rise to very 

 appreciable differential weighting; and (5) the contorted beds are 

 seldom very much softer or more mobile than the inclosing strata. 



CRYSTALLIZATION AND HYDRATION 



In certain types of rocks, like gypsum and salt, there is strong 

 evidence for the development of intraformational deformative 

 effects by crystallization (or hydration) after their deposition. In 

 the Zechstein salt of Germany, 



where the enclosing rocks are undisturbed, the layers of brightly colored bittern 

 salts and of gypsum often show a remarkable flexuous, sinuous, or disrupted 



character In the Sahna deposit of central New York, some of the 



alternating salt and gypsum layers occasionally show a pronounced flexing 

 and overfolding, while others are wholly undisturbed.' 



In his discussion of the salt beds of western central New York, 

 Luther^ has reproduced an interesting picture of a smaU sharply 

 overturned fold of rock salt between practically undisturbed beds. 



The above-described examples occur in regions of non-folded and 

 non-faulted strata, and it seems quite certain that "the main 

 force was the endogenetic one due to the crystallizing force of the 

 salts and to metasomatic process" (Grabau after Arrhenius). 



Very fine examples of corrugations and crenulations occur within 

 the gypsum deposits at Hillsborough, New Brunswick. According 

 to Ami^ "the gypsiferous deposits present evenly banded structure, 

 between which there occur neatly folded layers in the form of 

 ribbon-like corrugations" (Fig. 22). Kramm"* states that "the 

 gypsum rests upon a bottom of anhydrite and reaches a maximum 

 thickness of perhaps 125 feet," and that gypsum was derived by 



' A. W. Grabau, Principles of Stratigraphy (1913), p. 757. 



' D. D. Luther, N.Y. State Mus. Rept. so, Part 2 (1896), PI. 4. 



3H. M. Ami, Geol. Soc. Amer. Bull., Vol. XXV (1914), p. 37. 



4H. E. Kramm, Can. Geol. Surv., Guide Book No. i. Part 2 (1913), p. 364. 



